مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4076
Musnad of Abdullah bin Mas'ood
It was narrated that 'Abdullah said: We said: O Messenger of Allah, will one of us be blamed for what he did during the jahiliyyah? He said: "Whoever does well in Islam will not be blamed for what he did during the Jahiliyyah, but whoever does badly in Islam will be blamed for his earlier and later actions."
Musnad Ahmad 4103Its isnad is saheeh, Musiinn (120)]