Reference for Avodah Zarah 106:3

ואי תנא נפלה עליה מפולת משום דסבר הא מנחת כל אימת דבעינא לה שקילנא לה אבל גנבוה לסטים מדלא קא מהדר אבתרה בטולי בטלה צריכא

If it had taught the case where an avalanche fell on it, because he reasoned that [the idol] is lying there and whenever I want it I can take it [he did not annul it]; but in the case where robbers stole it, from the fact that he does not go searching for it [it might be assumed] that he had annulled it! Therefore it was necessary.

Jastrow