Sahih Muslim Book 31, Hadith Number 6048.

Abdullah b. Samit reported that Abu Dharr said: Son of my brother, I used to observe prayer two years before the advent of Allah’s Apostle (may peace be upon him). I said: To which direction did you turn your face? He said: To which Allah directed me to turn my face. The rest of the hadith is the same but with this addition that they went to a Kahin and his brother Unais began to praise him until he (in verses declared) him (Unais) as winner (in the contest of poetry), and so we got his camels, mixed them with our camels, and there is in this hadith also these words that Allah’s Apostle (may peace be upon him) came there and he circumambulated the House and observed two Rak’ahs of prayer behind the Station (of Ibrahim). I came to him and I was the first amongst persons to greet him with Assalam-O-‘Alaikum, and I said to Allah’s Messenger Let there be peace upon you. And he said: Let there be peace upon you too; who are you? And in the hadith (these words are) also found: Since how long have you been here? And Abu Bakr said: Let him be my guest tonight.