Musnad Ahmad 459:1

Yahya ibn Sa'id and Waki' narrated to us, they said: Hisham narrated to us, he said: Yahya ibn Abi Kathir narrated to us, from Muhammad ibn Ibrahim, from Khalid ibn Ma'dan, from al-Irbad ibn Sariyah: "That the Messenger of Allah, may Allah bless him and grant him peace, used to seek forgiveness for the first row three times, and for the second row once."