Abu Hurayrah reported that a man came to the prophet and asked, ''O messenger of Allah, who is most entitled to good companionship from me?'' the prophet replied: ''Your mother''. The man said. "Who is next?" The Prophet said, "Your mother." The man further said, "Who is next?" The Prophet said, "Your mother." The man asked for the fourth time, "Who is next?" The Prophet said, "Your father. "
(Related by Muslim and al-Bukhari)

Abu Hurayrah also narrated that the prophet said: ''Rubbed in dust is the nose, Rubbed in dust is the nose, Rubbed in dust is the nose of him {meaning, 'Shame and disgrace on him'} who is a live when one or both of his parents reach old age – and who then fails to enter paradise {by serving them and showing them kindness and compassion}''.
(Related by Muslim)