Musnad Ahmad 30:2447

Yahya ibn Sa'id narrated to us, from Ibn Abi Dhi'b, who said: Al-Aswad ibn al-'Ala' ibn Jariyah narrated to me, from Abu Salamah, from Abu Hurairah, from the Prophet, peace and blessings of Allah be upon him, who said: "From the moment one of you leaves his house for my mosque, one foot records a good deed, and the other erases a bad deed."