Musnad Ahmad 1153:1340

Muhammad ibn Bakr narrated to us, he said: Ibn Jurayj informed us, he said: Al-Zuhri informed me, regarding the hadith of ‘Urwah ibn al-Zubayr and Ibn al-Musayyib. ‘Urwah narrates from ‘Aishah, and Sa‘id ibn al-Musayyib from Abu Hurayrah: "That the Prophet, may Allah bless him and grant him peace, used to perform i‘tikaf during the last ten days of Ramadan, and he continued to do that until death took him, may Allah bless him and grant him peace." Abu ‘Abd al-Rahman said: I heard my father say: "This hadith is like this in the Book of Fasting, from Abu Hurayrah and ‘Aishah, and in [the Book of] I‘tikaf, it is from her alone."