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 5914
Sa'd b. Abi Waqqas reported that Allah's Messenger (may peace be upon him) left 'Ali b. Abi Talib behind him (as he proceeded) to the expedition of Tabuk, whereupon he ('Ali) said: Allah's Messenger, are you leaving me behind amongst women 4nd children? Thereupon he (the Holy Prophet) said: Aren't you satisfied with being unto me what Aaron was unto Moses but with this exception that there would be no prophet after me.