Zakaria, the son of Ibrahim, was a Christian. Later he converted to Islam and had the honor of meeting Imam Jafar Sadiq (A.S). He told Imam (A.S) “My mother is a Christian and she is old and blind.” The Imam advised him, “Serve your mother and behave kindly towards her. Upon her death, do not leave her dead body to others. Perform her funeral rites yourself.”
Thus this statement of the Imam (A.S) is pregnant with two prophecies. Her death and her conversion to Islam.
When Zakaria returned to Kufa he began to behave very kindly with his mother. He fed her with his own hands. Changed her clothes, washed and bathed her too. In short, he served his mother in every possible way. His mother asked, “My son you were not so dutiful when you were a Christian. Why is it that now you serve me day and night?”
Zakaria replied, “O my mother. I have a master who is the son of the Prophet of Allah (PBUH). He advised me to serve you in this way.” The mother asked, “Is he a prophet?” “No. But he is a son of the Prophet (PBUH).” “Such a person must be a Prophet because only prophets teach such manners.” The mother remarked.
Zakaria explained to his mother, “The chain of the Prophets came to an end with the Prophet of Islam (PBUH). He was the seal of the Prophets. The one who has guided me is the son of the Prophet (PBUH).” The mother said, “My son, the religion of Islam that you have embraced is better than all the religions. Teach me, so that I too may become a Muslim.”
So, Zakaria made her recite the ‘Kalima’ and taught her the true beliefs. Later, this lady performed the Zohrain and the Maghrebain prayers. The same night death approached her. She told her son: “Dear son, repeat to me again whatever you have taught me.” Zakaria began to recite while she listened carefully and in this way she passed away.
If the son or the daughter forgets the parents after their death and does not perform good deeds on their behalf, it is aq al-Walidayn’ irrespective of the fact that the child had fulfilled all his or her rights and served them till the time of their death.
Source: http://english.tebyan.net (Taken from Greater Sins – Volume 1 By: Ayatullah Abdul Hussein Dastaghaib Shirazi)