Musnad Abu Ya'la al-Mawsili 209:18

Husayn ibn al-Aswad narrated to us, Muhammad ibn Fudayl narrated to us, Abd al-Rahman ibn Ishaq narrated to us, from Hafsah bint Abi Kathir, from her father, Abu Kathir, who said: Umm Salamah taught me. She said: The Messenger of Allah (may Allah bless him and grant him peace) taught me. He said: "Say, O Umm Salamah, at the time of the Maghrib adhan: 'O Allah, at the approach of Your night, the departure of Your day, the voices of Your callers, and the attendance of Your prayers, I ask You to forgive me.'"