Sunan an-Nasa'i 3699
It was narrated that Ibn 'Abbas said:
"The Messenger of Allah said: 'It does not befit us to leave bad examples. The one who takes back his gift is like the dog which goes back to its vomit.'"
أَخْبَرَنَا عَمْرُو بْنُ زُرَارَةَ، قَالَ حَدَّثَنَا إِسْمَاعِيلُ، عَنْ أَيُّوبَ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏
"‏ لَيْسَ لَنَا مَثَلُ السَّوْءِ الْعَائِدُ فِي هِبَتِهِ كَالْكَلْبِ يَعُودُ فِي قَيْئِهِ ‏"‏ ‏.‏