Q 25: What is the textual proof from the Glorious Qur'an and the Prophetic Sunnah that a Muslim must be honest?
A--- Allah the Almighty says: {Alif-Lam-Mim (9) Do people think that they will be left alone because they say: "We believe, "and will not be tested. And We indeed tested those who were before them.
And Allah will certainly make (it) known (the truth of) those who are true, and will certainly make (it) known (the falsehood of)
those Who are liars} (10). (Al-'Ankabut, 1-3)
Prophet Muhammad (Peace be upon him) says: "Anyone who sincerely testifies that there is no god but Allah, and Muhammad is His Messenger will be delivered by Allah from the Hell-Fire ". (Bukhari and Muslim)
He (Peace be upon him) said to the Bedouin who asked him about the rituals of Islam and said (the Bedouin): 'By Allah! I will not do extra deeds or leave anything from it', he, Prophet Muhammad (Peace be upon him) said: 'He will be successful if he has told the truth'. (Bukhari and Muslim)
(9) These letters are one of the miracles of the Qur'an, and none but Allah (Alone) knows their meanings. (Translator)
(10) Although Allah knows all that before putting them to test. (Translator)
Reference: 200 FAQ On Muslims Belief - Shiekh Hafiz Ibn Ahmed Al Hakami