Narrated by Abu Bakra:
The Prophet. said, “The biggest of the great sins are: To join others in worship with Allah, to be undutiful to one’s parents, and to give a false witness.” He repeated it thrice, or said, “….a false statement,” and kept on repeating that warning till we wished he would stop saying it. (See Hadith No.7, Vol. 8) (Bukhari, Volume 9, Book 84, Number 54)
Narrated by ‘Abdullah bin ‘Amr:
A bedouin came to the Prophet and said, “O Allah’s Apostle! What are the biggest sins?: The Prophet said, “To join others in worship with Allah.” The bedouin said, “What is next?” The Prophet said, “To be undutiful to one’s parents.” The bedouin said “What is next?” The Prophet said “To take an oath ‘Al-Ghamus.” The bedouin said, “What is an oath ‘Al-Ghamus’?” The Prophet said, “The false oath through which one deprives a Muslim of his property (unjustly).” (Bukhari, Volume 9, Book 84, Number 55)