question #1 Sahih Muslim 90a, Book 1, Hadith 169 : What are the consequences of abusing one’s parents according to Islamic teachings?

Abusing one’s parents is one of the major sins. They (the hearers) said: Messenger of Allah, does a man abuse his parents too? He (the Holy Prophet) replied: Yes, one abuses the father of another man, who in turn abuses his father. One abuses his mother and he in turn abuses his (the former’s) mother.