كتاب الزكاة
12  
The Book of Zakat
(14)
Chapter: The virtue of spending and giving charity to relatives, spuses, children and parents, even if they are idolaters
(14)
باب فَضْلِ النَّفَقَةِ وَالصَّدَقَةِ عَلَى الْأَقْرَبِينَ وَالزَّوْجِ وَالْأَوْلَادِ وَالْوَالِدَيْنِ وَلَوْ كَانُوا مُشْرِكِينَ
Sahih Muslim 999

Maimuna bint Harith reported that she set free a slave-girl during the lifetime of the Messenger of Allah (ﷺ) and she made a mention of that to the Messenger of Allah (ﷺ) and he said:

Had you gives her to your maternal uncles, you would have a greater reward.
حَدَّثَنِي هَارُونُ بْنُ سَعِيدٍ الأَيْلِيُّ، حَدَّثَنَا ابْنُ وَهْبٍ، أَخْبَرَنِي عَمْرٌو، عَنْ بُكَيْرٍ، عَنْ كُرَيْبٍ، عَنْ مَيْمُونَةَ بِنْتِ الْحَارِثِ، أَنَّهَا أَعْتَقَتْ وَلِيدَةً فِي زَمَانِ رَسُولِ اللَّهِ صلى الله عليه وسلم فَذَكَرَتْ ذَلِكَ لِرَسُولِ اللَّهِ صلى الله عليه وسلم فَقَالَ ‏ "‏ لَوْ أَعْطَيْتِهَا أَخْوَالَكِ كَانَ أَعْظَمَ لأَجْرِكِ ‏"‏ ‏.‏
Reference : Sahih Muslim 999
In-book reference : Book 12, Hadith 54
USC-MSA web (English) reference : Book 5, Hadith 2187
  (deprecated numbering scheme)