Zuhayr bin Harb زهير بن حرب بن شداد أبو خثيمة · The Book of Purification and its Sunnah

"I heard my father say: 'I entered upon 'Aishah, and I heard her say: "When the Messenger of Allah exited the toilet, he would say: Ghufranaka (I seek Your forgiveness).'" (Sahih) Another chain with similar wording.