Musannaf Ibn Abi Shayba 27:578

Muhammad ibn Bishr narrated to us, he said: Isma'il ibn Abi Khalid narrated to me, from Shu'ayb ibn Yasar, from 'Ikrimah, who said: The Messenger of Allah (may Allah bless him and grant him peace) called for Ibn 'Abbas and seated him on his lap. He wiped over his head and prayed for him to have knowledge.