Narrated ‘Abdullah bin ‘Amr:
Allah’s Apostle said. “It is one of the greatest sins that a man should curse his parents.” It was askedĀ (by the people), “O Allah’s Apostle! How does a man curse his parents?” The Prophet said, “‘The manĀ abuses the father of another man and the latter abuses the father of the former and abuses his mother.”
Sahih Bukhari, Volume 8, Book73, Number 4