Sahih Bukhari Volume 3, Book 47, Hadith Number 789.

Narated By Asma’ bint Abu Bakr : My mother came to me during the lifetime of Allah’s Apostle and she was a pagan. I said to Allah’s Apostle (seeking his verdict), “My mother has come to me and she desires to receive a reward from me, shall I keep good relations with her?” The Prophet said, “Yes, keep good relation with her.”