Being good to parents is the greatest [and most important] duty.
Once the Prophet (Sallallaho alaihe wasallam) spent a sleepless night. He would turn from side to side and could not sleep. His wife asked him: “O Prophet of Allah! Why can you not sleep?” He responded: “A date was lying about. I took it up and ate it, lest it should be wasted. Now I am troubled lest it might be from Sadaqah.” Most probably the date belonged to the Prophet himself, but because people sent him their ‘Sadaqah’ as well (for distribution), he could not sleep with the apprehension that it might be of Sadaqah. This is the last word in scruples from the master himself, that he could not sleep because of a suspicion in his mind. How would it go with those who claim themselves to be the slaves of that very master but indulge in usury, corruption, theft, plunder and every other type of ‘haraam’ business without the least scruple.
The Prophet (Sallallaho alaihe wasallam) said: “My Lord offered to turn the mounts of Mecca into gold for me. But my supplication to Him was; ‘0, Allah! I like to eat one day and feel hungry the next, so that I may cry before Thee and remember Thee when I am hungry; and be grateful to Thee and glorify Thee when my hunger is gone!” Thus said our Prophet ‘(Sallallaho alaihe wasallam). We profess to follow him and are proud of being in the fold of his Ummat. Isn’tit incumbent upon us to follow him in practice also?
Surah An-Nisa, Verse 86:
And when you are greeted with a greeting, greet with a better (greeting) than it or return it; surely Allah takes account of all things.
Whoever is good to his parents, his child will be good to him.