Mishkat al-Masabih #3617

‘Abdallah b. Unais reported God’s Messenger as saying, “Among the most serious of major sins are attributing a partner to God, unfilial behaviour, and deliberate perjury. If anyone swears an oath which he is compelled to take (or a firm oath) and introduces into it as much falsehood as a gnat’s wing, a spot will be put in his heart till the day of resurrection.” Tirmidhi transmitted it, saying this is a gharib tradition.