Musnad Ahmad 26:49

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Shaqiq, from Abdullah, who said: A man came to the Prophet, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, if I do good in Islam, will I be held accountable for what I did during the Jahiliyyah (pre-Islamic period)?" He said: "If you do good in Islam, you will not be held accountable for what you did during the Jahiliyyah. But if you do evil in Islam, you will be held accountable for the first and the last."