It is narrated from Sayyiduna Abdullah bin Unais that the Messenger of Allah, peace and blessings be upon him, said: Among the major sins, the greatest sin is associating partners with Allah, disobedience to parents, and taking a false oath. And if even as much as the wing of a mosquito of falsehood is included in it, Allah places a mark on his heart until the Day of Resurrection.
Hadith Referenceمسند احمد / مسند المكيين / 16043
Hadith Gradingحکم دارالسلام:صحيح دون قوله: «وما حلف حالف بالله يمينا» وهذا إسناد ضعيف لضعف هشام بن سعد