Musannaf Ibn Abi Shayba 16:231

Abu Bakr narrated to us, he said: Ibn ‘Uyaynah narrated to us, from ‘Amr, from Sa‘id ibn Huwayrith: I heard Ibn ‘Abbas saying: We were with the Prophet, may Allah bless him and grant him peace, and he came from the privy (al-gha’it), and food was brought to him. It was said to him: "Will you not perform ablution?" He said: "I am not about to pray, so that I should perform ablution."