Maliks Muwatta Book 2, Hadith Number 50.
Section : How to Wipe over Leather Socks.
Yahya related to me from Malik from Yazid ibn Abdullah Qusayt al-Laythi that he saw Said ibn al-Musayyab having a nose-bleed while praying. He went off to the room of Umm Salama, the wife of the Prophet, may Allah bless him and grant him peace, and water was brought to him and he did wudu. He then returned and completed his prayer.