"I said: 'O Messenger of Allah! Who most deserves(my) reverence?' He said: 'Your mother.'" He said: "I said: 'Then who?' He said: 'Your mother.'" He said: "I said: 'Then who?' He said: 'Your mother.'" He said: "I said: 'Then who?' He said: 'Then your father, then the nearest relatives, then the nearest relatives.'"
Jami` at-Tirmidhi Book 27, Hadith 1