'Ata' ibn Yasar said that a man came to Ibn 'Abbas and said, "I asked a woman to marry me and she refused to marry me. Another man asked her and she agreed to marry him. I became jealous and killed her. Is there any way for me to repent?" 
He asked, "Is your mother alive?" "No," he replied. 
He said, "Repent to Allah Almighty and try to draw near Him as much as you can."

'Ata' said, "I went to Ibn 'Abbas and asked him, 'Why did you ask him whether his mother was alive?' 
He replied, 'I do not know of any action better for bringing a person near to Allah than dutifulness to his mother.'"

 
[Adab Al-Mufrad - Imam Al Bukhari - I.2.#4]