Musnad Ahmad 25:400

'Affan narrated to us, Wuhayb narrated to us, Musa ibn Salim Abu Jahdam narrated to us, 'Abdullah ibn 'Ubaydullah ibn 'Abbas narrated to us, he said: I and some youths from Quraysh entered upon Ibn 'Abbas. He said: So they asked him, "Did the Messenger of Allah, peace and blessings of Allah be upon him, recite in the Dhuhr and 'Asr [prayers]?" He said: "No." He said: So they said, "Perhaps he was reciting to himself?" He said: "A scratch [i.e., a rebuke]! This is worse. The Messenger of Allah, peace and blessings of Allah be upon him, was a commanded servant; he conveyed what he was sent with. And he did not single us out, to the exclusion of the people, except with three things: He commanded us to perform the ablution perfectly, not to eat from the charity, and not to mount a donkey upon a mare."