Musnad Ahmad 1060:51

'Abd al-Rahman ibn Mahdi narrated to us, Malik narrated to us, from Zayd ibn Aslam, from Ibrahim ibn 'Abd Allah ibn Hunayn, from his father, who said: Al-Miswar ibn Makhramah and Ibn 'Abbas differed regarding the pilgrim in the state of ihram washing his head. Ibn 'Abbas said: "He may wash it," and Al-Miswar said: "He may not wash it." They sent me to Abu Ayyub, and I asked him. He poured water over his head, then brought his hands forward and moved them backward. Then he said: "This is how I saw the Prophet, may Allah bless him and grant him peace, do."