Imam Malik's Muwatta, Chapter: Purity

Yahya related to me from Malik from Nafi that she saw Safiyya bint Abi Ubayd, the wife of Abdullah ibn 'Umar, take off her head-covering and wipe her head with water. Nafi was a child at the time. Malik was asked about a man who did wudu but forgot to wipe his head until the water had dried. He said, "I consider that he should wipe his head and then repeat the prayer if he has already performed it." Malik was asked about a man who did wudu but forgot to wipe his head until the water had dried. He said, "I consider that he should wipe his head and then repeat the prayer if he has already performed it."