Sahih Muslim
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-Fadail Al-Sahabah)
Book Number: 031 / Hadith Number: 5961
Abdullah b. Ja'far reported that when Allah's Messenger (may peace be, upon him) came back from a journey, the children of his family used to accord him welcome. It was in this way that once he came back from a journey and I went to him first of all. He mounted me before him. Then there came one of the two sons of Fatima and he mounted him behind him and this is how we three entered Medina riding on a beast.