Musnad Ahmad 30:3073

Waki’ narrated to us, he said: Ibn Abi Dhi’b narrated to us, from al-Aswad ibn al-‘Ala’ ibn Jariyah, from Abu Salamah, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "From the moment one of you leaves his house to my mosque, one foot writes a good deed, and one foot erases a bad deed."