Musannaf Ibn Abi Shayba 21:648

Abu Amir al-Aqdi narrated to us, from Ali ibn Mubarak, from Yahya ibn Abi Kathir, from Muhammad ibn Abd al-Rahman, that Abdullah ibn Salam, when he entered the mosque, would greet the Prophet, may Allah bless him and grant him peace, and say: "O Allah, open for me the doors of Your mercy." And when he exited, he would greet the Prophet, may Allah bless him and grant him peace, and seek refuge from Satan.