Musnad Abu Ya'la al-Mawsili 111:121

Abu Khaythama narrated to us, Makhlad ibn Yazid al-Harrani narrated to us, Ibn Jurayj narrated to us, from Muhammad ibn Yusuf, from Sulayman ibn Yasar, from Ibn Abbas: That he saw Abu Hurayrah while he was performing ablution (wudu). He said, "O Ibn Abbas, do you know from what I am performing ablution? From pieces of dried yogurt (aqt) that I ate." He (Ibn Abbas) said, "By Allah, I do not know from what you performed ablution. As for me, I saw the Messenger of Allah (peace be upon him) eat bread and meat, then he stood for prayer and did not perform ablution."