Understanding Usul Al-Fiqh by Abu Tariq Hilal - Abu Ismael al-Beirawi

There are two definitions of a Sahabi:

1. A Muslim who saw the Prophet (saw).

2. A Muslim who lived with the Prophet (saw) for one or two years or participated in one or two Ghazwaat (military expeditions led by the Prophet [saw]).

The latter definition was reported by the famous scholar of the Tabi‟een, Said bin al-Musayeb and is stronger. It has been narrated he said, “It is essential that someone has companionship with the Prophet (saw) for one or two years, or has gone out with him on one or two battles.” Shu'ba reported from Musa al-Sibillani - whom he spoke appreciatively about - that he said: “I said to Anas bin Malik (ra). Are there any companions of the Messenger of Allah (saw) left other than you? He said: There are still many Arabs who saw him. As for his companions, no!” Imam al-Mazini said in his book Sharh ul-Burhan, “We do not mean by Sahabah those who met him for a day or two, or those who attended him for some business and then left, we mean those who followed him, helped him and were guided by the light that Allah (swt) revealed to him (saaw), those are the ones to attain felicity.”