Musnad Abu Ya'la al-Mawsili 154:184

Shayban narrated to us, Harb ibn Surayj al-Minqari narrated to us, Ayyub al-Sakhtiyani narrated to us, from Nafi’, from Ibn ‘Umar, who said: We used to refrain from seeking forgiveness for the people of major sins until we heard the Messenger of Allah (may Allah bless him and grant him peace) say: "Indeed, Allah does not forgive that partners be associated with Him, but He forgives what is less than that for whom He wills" (An-Nisa). He said: "I have reserved my supplication as an intercession for the people of major sins from my nation." He said: So we refrained from much of what was in our minds, then we spoke afterward and hoped.