Musnad Ahmad 1153:1159

Abu Amir narrated to us, Sa'id ibn Muslim narrated to us, he said: I heard 'Amir ibn 'Abdullah ibn al-Zubayr, he said: 'Awf ibn al-Harith ibn al-Tufayl narrated to me, that 'Aisha informed him that the Prophet, peace and blessings of Allah be upon him, used to say: "O 'Aisha, beware of the belittled sins, for indeed there is a seeker for them from Allah, the Almighty and Majestic."