Musnad Ahmad 25:206

Ja'far ibn 'Awn narrated to us, Ibn Jurayj informed us, from 'Ata', who said: We were present with Ibn 'Abbas at the funeral of Maymunah, the wife of the Prophet, may Allah bless him and grant him peace, at Sarif. Ibn 'Abbas said: "This is Maymunah. When you lift her bier, do not shake it and do not jolt it, for the Messenger of Allah, may Allah bless him and grant him peace, had nine wives. He used to divide [his time] among eight, and there was one for whom he did not divide." 'Ata' said: The one for whom he did not divide was Safiyyah.