Musnad Ahmad 1153:1202

Hashim ibn al-Qasim narrated to us, Isra'il narrated to us, from Yusuf ibn Abi Burdah, from his father, who said: 'A'ishah narrated to me that the Prophet, peace and blessings of Allah be upon him, used to say when he exited the privy: "Your forgiveness (Ghufranaka)."