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Ibn 'Abbas reported that the Prophet, may Allah bless him and grant him peace, said, "We do not give a bad example. The one who takes back his gift is like the dog who returns to his own vomit."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا أَبُو نُعَيْمٍ، قَالَ: حَدَّثَنَا سُفْيَانُ، عَنْ أَيُّوبَ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ: لَيْسَ لَنَا مَثَلُ السَّوْءِ، الْعَائِدُ فِي هِبَتِهِ، كَالْكَلْبِ يَرْجِعُ فِي قَيْئِهِ.
sunnah.com