They traced the hadith back to the Prophet ﷺ, who said, "It is not permissible for a man to give a gift and then take it back, except for a father with regard to what he gives his child."
حدثنا محمد بن بشار وأبو بكر بن خلاد الباهلي قالا حدثنا ابن أبي عدي عن حسين المعلم عن عمرو بن شعيب عن طاوس
يرفعان الحديث إلى النبي ﷺ قال لا يحل للرجل أن يعطي العطية ثم يرجع فيها إلا الوالد فيما يعطي ولده
[Its isnad is sahih] Tirmidhi transmitted it in the Book of Business Transactions, in the chapter on the dislike of retracting a gift, 2132, from Muhammad bin Bashshar with this wording, and he said, hasan sahih. Ibn Jarud graded it sahih, 1299, and it was also transmitted by Ibn Hibban, 994, and Hakim, 2/46, and Dhahabi agreed with him.