As Muslims it is our duty to keep ourselves away from all sins; minor and major. This is based on the fact that the first priority for Muslims is to gain the pleasure of Allah the Almighty by doing what He likes and avoiding what He dislikes, irrespective of the gravity or the simplicity of the sin.
The first commandment in Islam as revealed to all the prophets is to worship Allah the Almighty and immediately after this comes the duty of being dutiful to parents
{Thy Lord has decreed, that you worship none save Him, and (that you show) kindness to parents.} (Al-Israa 17: 23).
Thus, Islam urges every Muslim to be dutiful to his parents, extending to them the kindest treatment possible.
Failing to treat parents kindly makes the person guilty of disobedience to parents as well as to Allah the Almighty.
Doing so may deprive him of the chance of being admitted to Paradise. Therefore, it goes without saying that disobedience to parents or mistreating them is the second major sin after Shirk (associating other beings with Allah).
The Prophet (peace and blessings be on him) was asked about the greatest sins. He said, “To join partners in worship with Allah; to kill a soul which Allah has forbidden to kill; and to be undutiful or unkind to one’s parents…“(Bukhari)
In another tradition, the Prophet (peace and blessings be on him) said, “The person who severs the bond of kinship will not enter Paradise.” (Al-Bukhari)
He also said, “The pleasure of Allah is in the pleasure of one’s parents and the wrath of Allah is in the wrath of one’s parents.” (Ibn Hibban)