Haɗin kai (Ash-Sharika) a harshen Larabci yana nufin haɗa hannun jari biyu ko fiye tare ta yadda babu ɗayansu da za a iya rarrabewa da ɗayan. A Shari'a, haɗin kai yarjejeniya ce tsakanin mutum biyu ko fiye, inda suka amince su yi aikin kuɗi da niyyar samun riba. Yarjejeniyar haɗin kai na buƙatar kasancewar tayi da karɓa, kamar yadda yake ga dukkan yarjejeniyoyin Musulunci. Tayi takan faru ne idan wani ɓangare ya ce wa ɗayan: "Na shiga haɗin kai da kai a kan kaza da kaza," sannan ɗayan ya amsa da cewa, "Na karɓa." Ba wajibi ba ne a yi amfani da waɗannan kalmomi daidai, amma ma'anar ita ce abin da ake buƙata. Dole ne a sami wani abu a cikin tayi da karɓa da zai nuna cewa ɗaya daga cikin ɓangarorin ya yi magana da ɗayan, da baki ko a rubuce, a kan batun haɗin kai a kan wani abu, ɗayan kuma ya karɓa. Saboda haka, yarjejeniyar haɗin kai kawai ba ta zama yarjejeniya ba. Haka nan, yarjejeniyar biyan kuɗi ko dukiya domin haɗin kai ba a ɗaukarta a matsayin yarjejeniya ba. Maimakon haka, dole ne yarjejeniyar ta ƙunshi ra'ayin haɗin kai a cikin wani abu. Sharadin ingancin yarjejeniyar haɗin kai a Musulunci shi ne cewa abin da aka yi yarjejeniya a kansa ya zama haƙƙin tasarruf, kuma wannan haƙƙin tasarruf, wanda aka kulla yarjejeniyar haɗin kai a kansa, ya dace da wakilci (Wakala), ta yadda abin da aka samu ta hanyar tasarrufin ya zama tsakanin ɓangarorin biyu.

Company (Ash-Sharika) linguistically means mixing two or more shares together such that neither can be distinguished from the other. Company in Shar’a is a contract between two or more persons, in which they agree to perform financial work with the intention of making profit. The contract of the company requires the existence of both offer and acceptance, as is the case with all Islamic contracts. An offer occurs when one party says to the other: ‘I entered into partnership with you in such and such’ and the other party replies by saying, ‘I accepted.’ These actual words are not necessary but the meaning is. There must occur in the offer and acceptance something that indicates that one of the parties addressed the other orally or in writing on the matter of partnership over something, and the other accepted. Therefore, an agreement on partnership only does not represent a contract. An agreement to pay money or property for partnership is also not considered a contract as well. Rather, the contract must include the concept of partnership in something. The condition of validity of the partnership contract in Islam requires that the contracted matter be a right of disposal and that this right of disposal, over which the company contract is concluded, is suitable for representation (Wakala) such that what is gained by the disposal is shared between the two partners.

Haɗin gwiwa a Musulunci halal ne, domin lokacin da aka aiko Annabi Muhammadu (SAW) a matsayin Manzo, mutane suna mu'amala da kamfanoni, shi kuma bai hana hakan ba. Al-Bukhari ya ruwaito cewa Abu Al-Minhal ya ce: "Ni da abokin haɗin gwiwata mun sayi wani abu da tsabar kuɗi da kuma bashi. Al-Bara ibn 'Azib ya zo wurinmu, sai muka tambaye shi game da haka. Ya ce: 'Abokin haɗin gwiwata, Zaid ibn Al-Arqam, da ni mun yi irin haka, sai muka tambayi Annabi ﷺ game da haka. Ya ce: "Abin da ke da tsabar kuɗi, ku ɗauka, abin da ke da bashi kuma, ku mayar da shi."'" Ad-Daraqutni ya ruwaito daga Abu Hurairah cewa Annabi ﷺ ya ce: "Allah Mai Girma ya ce: 'Ni ne na uku ga abokan haɗin gwiwa biyu muddin ɗayansu bai yaudari abokinsa ba. Idan ya yaudare shi, zan fita daga tsakaninsu.'" Haɗin gwiwa halal ne a tsakanin Musulmi, da Ahlul Dhimmah (waɗanda ba Musulmi ba waɗanda ke zaune ƙarƙashin ikon Musulunci), da kuma tsakanin Musulmi da Ahlul Dhimmah. Don haka halal ne Musulmi ya shiga haɗin gwiwa da Kirista, mai bautar wuta ko sauran Ahlul Dhimmah. Muslim ya ruwaito daga Abdullah ibn 'Umar, wanda ya ce: "Annabi ﷺ ya yi mu'amala da mutanen Khaibar, waɗanda Yahudawa ne, ta hanyar raba rabin amfanin ƙasar, na shuka ko 'ya'yan itace." A wata ruwaya ta Bukhari daga Aisha: "Annabi ﷺ ya sayi abinci daga wani Bayahude a Madina, kuma ya ajiye masa makamansa a matsayin tabbaci." At-Tirmidhi ya ruwaito daga Ibn 'Abbas, wanda ya ce: "Annabi ﷺ ya rasu alhali an ajiye makamansa a matsayin tabbaci saboda sa'o'i ashirin na abinci da ya karɓa don iyalansa." At-Tirmidhi ya ruwaito daga Aisha cewa "Manzon Allah ﷺ ya aika ga wani Bayahude yana neman tufafi biyu (kuma ya jira) har zuwa lokacin samun wadata." Saboda haka, shiga haɗin gwiwa da Yahudawa da Kiristoci da sauran Ahlul Dhimmah halal ne, domin mu'amala da su halal ce. Sai dai, Ahlul Dhimmah ba sa izinin sayar da giya da naman alade yayin da suke abokan haɗin gwiwa da Musulmi. Kafin ya shiga haɗin kasuwanci da Musulmi, wani Dhimmi zai iya kasancewa yana sayar da giya, kuma kuɗin da ya samu daga hakan zai zama halal ga kamfanin. Haɗin kasuwanci yana da inganci ne kawai tsakanin mutanen da aka yarda su yi tasarruf da dukiyarsu, domin yarjejeniya ce da ta dogara da tasarrufin dukiya. Saboda haka, bai halatta a kafa kamfani da mutumin da aka hana shi yin tasarruf da dukiya ba. Haka kuma, ba a yarda a shiga haɗin kasuwanci da mutumin da aka sanya wa waliyyi ba, ko mutumin da ba a yarda da tasarrufinsa ba.

Partnership is allowed in Islam because when Muhammad (pbuh) was sent as a Messenger people were dealing with companies and He (pbuh) did not forbid this. Al Bukhari narrated that Abu Al-Minhal said: “I and my partner bought something in cash and credit. Al-Bara ibn ‘Azib came to us so we asked Him about this. He said: ‘My partner, Zaid ibn Al-Arqam, and I did the same and we asked the Prophet (pbuh) about this.’ He (pbuh) said: ‘That which is in cash you take, and that which is in credit you return it back.”’ Ad-Daraqutni narrated from Abu Hurairah that the Prophet (pbuh) said: “Allah the Supreme said ‘I am the third of the two partners as long as one of them does not betray his companion. If He betrayed, I would withdraw from them.”’ Partnership is allowed amongst Muslims, Dhimmis (non-Muslims living under Islamic authority), and between Muslims and Dhimmis. So it is allowed for a Muslim to enter into partnership with a Christian, a fireworshipper or other Dhimmis. Muslim narrated from Abdullah ibn ‘Umar who said: ‘The Prophet (pbuh) dealt with the people of Khaybar, who were Jews, for half of the land production of plant or fruit.’ In another narration by Bukhari from Aisha: “The Prophet (pbuh) bought food from a Jew in Madinah and He deposited his armour with Him as security.” At-Tirmidhi narrated from Ibn ‘Abbas who said ‘The Prophet (pbuh) passed away while his armour was left as a security in return for twenty cubic measures (Sa’a) of food which He took for his family.’ At-Tirmidhi narrated from Aisha that ‘the Messenger of Allah (pbuh) sent for a Jew asking Him for two garments (and to wait) until (the time of) prosperity.’ Entering into partnership with Jews and Christians and other Dhimmis is therefore allowed, as dealing with them is permissible. However, Dhimmis are not allowed to sell alcohol and pork while acting as partners with Muslims. Prior to forming a partnership with a Muslim, a Dhimmi may have sold alcohol, the proceeds of which would be Halal for the company. Partnership is only valid between people whose right of disposal is allowed, for it is a contract based upon the disposal of property. It follows that it is invalid to form a company with a person who is prevented from disposal of property. It is also not allowed to enter into partnership with a person who is placed under guardianship, or a person whose right of disposal is not allowed.

Shirka ta kasu zuwa shirkar dukiya ko shirkar kwangila. Shirkar dukiya ita ce shirkar kadarori, kamar zama abokin mallakar wata dukiya da aka gada, aka saya, ko aka ba da kyauta. Shirkar kwangila ita ce batun da ake tattaunawa a kai dangane da karuwar mallaka. Daga nazarin kwangilolin shirka a Musulunci, da hukunce-hukuncen shari'a (Ahkam Shar'iyah) da ke da alaka da su, ana iya cewa akwai nau'o'in shirka guda biyar a Musulunci. Su ne: Al-'Inan (daidaito), Al-Abdan (jiki/aiki), Al-Mudharaba (biyu ko fiye), Al-Wujooh (fuska/daraja) da Al-Mufawadha (tattaunawa).

Partnership is either a partnership of properties or a partnership of contracts. The company of properties is a company of assets, such as partnership in a property that has been inherited, bought or gifted. The company of contracts is the subject of discussion regarding increasing of ownership. From the examination of partnership contracts in Islam, and the divine rules (Ahkam Shar’iyah) related to them it can be concluded that there are five types of company in Islam. These are Al-’Inan (equal), Al- Abdan (bodies), Al-Mudharaba (two or more), Al-Wujooh (faces) and Al- Mufawadha (negotiation).