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 1003 b

Asma' bint Abu Bakr reported:

My mother who was a polytheist came to me when he (the Holy Prophet) entered into treaty with, the Quraish (of Mecca). I inquired from the Messenger of Allah (ﷺ) saying: Messenger of Allah, there has come to me my mother and she is inclined; should I (in this state of her mind) show her kindness? He said: Yes, treat her kindly.
وَحَدَّثَنَا أَبُو كُرَيْبٍ، مُحَمَّدُ بْنُ الْعَلاَءِ حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ هِشَامٍ، عَنْ أَبِيهِ، عَنْ أَسْمَاءَ بِنْتِ أَبِي بَكْرٍ، قَالَتْ قَدِمَتْ عَلَىَّ أُمِّي وَهِيَ مُشْرِكَةٌ فِي عَهْدِ قُرَيْشٍ إِذْ عَاهَدَهُمْ فَاسْتَفْتَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم فَقُلْتُ يَا رَسُولَ اللَّهِ قَدِمَتْ عَلَىَّ أُمِّي وَهْىَ رَاغِبَةٌ أَفَأَصِلُ أُمِّي قَالَ ‏ "‏ نَعَمْ صِلِي أُمَّكِ ‏"‏ ‏.‏
Reference : Sahih Muslim 1003b
In-book reference : Book 12, Hadith 62
USC-MSA web (English) reference : Book 5, Hadith 2195
  (deprecated numbering scheme)