Sahih Bukhari Volume 5, Book 59, Hadith Number 522.

Narrated By Anas bin Malik : We arrived at Khaibar, and when Allah helped His Apostle to open the fort, the beauty of Safiya bint Huyai bin Akhtaq whose husband had been killed while she was a bride, was mentioned to Allah’s Apostle. The Prophet selected her for himself, and set out with her, and when we reached a place called Sidd-as-Sahba,’ Safiya became clean from her menses then Allah’s Apostle married her. Hais (i.e. an ‘Arabian dish) was prepared on a small leather mat. Then the Prophet said to me, “I invite the people around you.” So that was the marriage banquet of the Prophet and Safiya. Then we proceeded towards Medina, and I saw the Prophet, making for her a kind of cushion with his cloak behind him (on his camel). He then sat beside his camel and put his knee for Safiya to put her foot on, in order to ride (on the camel).