The Book Pertaining to the Merits of the Companions (Allah Be Pleased With Them) of the Holy Prophet (May Peace Be Upon Him) (Kitab Al-Fada'il Al-Sahabah)
Muslim :: Book 31 : Hadith 6178
Abu Huraira reported: We were sitting in the company of Allah's Apostle (may peace be upon him) that Sura al-Jumu'a was revealed to him and when he recited (these words):" Others from amongst them who have not yet joined them," a person amongst them (those who were sitting there) said: Allah's Messenger! But Allah's Apostle (may peace be upon him) made no reply, until he questioned him once, twice or thrice. And there was amongst us Salman the Persian. The Apostle of Allah (may peace be upon him) placed his hand on Salman and then said: Even if faith were near the Pleiades, a man from amongst these would surely find it.