Musnad Ahmad 1154:7

Aswad ibn Amir narrated to us, he said: Al-Hasan—meaning Ibn Salih—narrated to us, from Layth, from Abdullah ibn al-Hasan, from Fatimah bint Husayn, from Fatimah, daughter of the Prophet, may Allah bless him and grant him peace, from the Prophet, may Allah bless him and grant him peace, she said: When he would enter the mosque, he would invoke blessings upon Muhammad and grant him peace, then he would say: "O Allah, forgive my sins and open for me the doors of Your mercy." And when he would exit, he would invoke blessings upon Muhammad and grant him peace, and he would say: "O Allah, forgive my sins and open for me the doors of Your bounty."