Musannaf Ibn Abi Shayba 33:1421

Muhammad ibn Mus’ab narrated to us, he said: Al-Awza’i narrated to us, from Yahya ibn Abi Kathir, that ‘Abdullah ibn Salam struck a servant of his with a strike, so he began to weep and say, "Take retribution from me." And the servant said, "I will not take retribution from you, my master." Ibn Salam said, "Every sin Allah forgives, except for a strike to the face."