Maliks Muwatta Book 42, Hadith Number 3.

Yahya related to me from Malik from Ibn Shihab that he was asked about the hadd of the slave for wine. He said, “I heard that he has half the hadd of a freeman for drinking wine. Umar ibn al-Khattab, Uthman ibn Affan, and Abdullah ibn Umar flogged their slaves with half of the hadd of a freeman when they drank wine.”