Abu Huraira reported that a person came to Allah's Messenger (may peace be upon him) and said: Who among the people is most deserving of a fine treatment from my hand? He said: Your mother. He again said: Then who (is the next one)? He said: Again it is your mother (who deserves the best treatment from you). He said: Then who (is the next one)? He (the Holy Prophet) said: Again, it is your mother. He (again) said: Then who? Thereupon he said: Then it is your father.
Narrated in Saheeh Muslim, Book 032, Number 6180 - Sunni Hadith