Asim bin Kulayb said: I heard Iyad bin Marthad, or Marthad bin Iyad, al-Amiri relating to a man that he asked the Prophet (peace and blessings be upon him) about a deed that would admit him to Paradise. He (peace and blessings be upon him) said: "Is either of your parents alive?" He said: No. He (peace and blessings be upon him) asked him three times, then said: "Give water to drink: carry it to them when they are absent, and spare them the trouble of it when they are present."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15084