صحيح البخاري Sahih Bukhari كتاب الهبة The Book of Gifts and The Superiority of Giving Gifts and The Exhortation for Giving Gifts
بَابُ إِذَا حَمَلَ رَجُلٌ عَلَى فَرَسٍ فَهْوَ كَالْعُمْرَى وَالصَّدَقَةِ:

(37) Chapter. If somebody gives another person a horse (as a gift) then the rule is the same as that concerning the Umra or Sadaqa (i.e., the giver has no right to claim restitution).

2 hadith
Hadith Q2636
وَقَالَ بَعْضُ النَّاسِ لَهُ أَنْ يَرْجِعَ فِيهَا .
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Hadith Reference Sahih Bukhari / The Book of Gifts and The Superiority of Giving Gifts and The Exhortation for Giving Gifts / Hadith: Q2636
Hadith 2636
حَدَّثَنَا الْحُمَيْدِيُّ ، أَخْبَرَنَا سُفْيَانُ ، قَالَ : سَمِعْتُ مَالِكًا يَسْأَلُ زَيْدَ بْنَ أَسْلَمَ ، قَالَ : سَمِعْتُ أَبِي ، يَقُولُ ، قَالَ عُمَرُ رَضِيَ اللهُ عَنْهُ : حَمَلْتُ عَلَى فَرَسٍ فِي سَبِيلِ اللهِ ، فَرَأَيْتُهُ يُبَاعُ ، فَسَأَلْتُ رَسُولَ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ ، فَقَالَ : " لَا تَشْتَرِهِ ، وَلَا تَعُدْ فِي صَدَقَتِكَ " .
Narrated `Umar bin Al-Khattab: Once I gave a horse (for riding) in Allah's Cause. Later I saw it being sold. I asked Allah's Apostle (whether I could buy it). He said, "Don't buy it, for you should not get back what you have given in charity."
Hadith Reference Sahih Bukhari / The Book of Gifts and The Superiority of Giving Gifts and The Exhortation for Giving Gifts / Hadith: 2636
Hadith Grading محدثین: أحاديث صحيح البخاريّ كلّها صحيحة