Musnad Ahmad 26:536

Yahya narrated to us, from Sufyan, Mansur and Sulayman narrated to us, from Abu Wa'il, from Abdullah, who said: A man said: "O Messenger of Allah, shall we be held accountable for what we did during the Jahiliyyah (pre-Islamic period)?" He said: "If you do good, you will not be held accountable. But if you do evil in Islam, you will be held accountable for the first and the last."