Language:
كتاب الزكاة
24  
Obligatory Charity Tax (Zakat)
(59)
Chapter: Can one buy the thing which he has given in charity?
(59)
باب هَلْ يَشْتَرِي صَدَقَتَهُ
Sahih al-Bukhari 1489

Narrated `Abdullah bin `Umar:

`Umar bin Al-Khattab gave a horse in charity in Allah's Cause and later he saw it being sold in the market and intended to purchase it. Then he went to the Prophet (ﷺ) and asked his permission. The Prophet said, "Do not take back what you have given in charity." For this reason, Ibn `Umar never purchased the things which he had given in charity, and in case he had purchased something (unknowingly) he would give it in charity again.

حَدَّثَنَا يَحْيَى بْنُ بُكَيْرٍ، حَدَّثَنَا اللَّيْثُ، عَنْ عُقَيْلٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ ـ رضى الله عنهما ـ كَانَ يُحَدِّثُ أَنَّ عُمَرَ بْنَ الْخَطَّابِ تَصَدَّقَ بِفَرَسٍ فِي سَبِيلِ اللَّهِ فَوَجَدَهُ يُبَاعُ، فَأَرَادَ أَنْ يَشْتَرِيَهُ، ثُمَّ أَتَى النَّبِيَّ صلى الله عليه وسلم فَاسْتَأْمَرَهُ فَقَالَ ‏ "‏ لاَ تَعُدْ فِي صَدَقَتِكَ ‏"‏ فَبِذَلِكَ كَانَ ابْنُ عُمَرَ ـ رضى الله عنهما ـ لاَ يَتْرُكُ أَنْ يَبْتَاعَ شَيْئًا تَصَدَّقَ بِهِ إِلاَّ جَعَلَهُ صَدَقَةً‏.‏
Reference : Sahih al-Bukhari 1489
In-book reference : Book 24, Hadith 89
USC-MSA web (English) reference : Vol. 2, Book 24, Hadith 566
  (deprecated numbering scheme)