Beautiful Hadith is about Parents

'Abdullah bin 'Amr bin Al-'as RA reported: Messenger of Allah (peace be upon him) said, "It is one of the gravest sins to abuse one's parents." It was asked (by the people): "O Messenger of Allah, can a man abuse his own parents?" Messenger of Allah (peace be upon him) said, "He abuses the father of somebody who, in return, abuses the former's father; he then abuses the mother of somebody who, in return, abuses his mother" (Bukhari and Muslim)