Explanation

Ibn Mas‘ūd (may Allah be pleased with him) said: My swearing by Allah about something I am lying about, assuming that this might happen, is more beloved to me than swearing by anything other than Allah about something I am truthful about. Thus, he gave precedence to swearing by Allah while lying over swearing by other than Him while being truthful. This is because swearing by Allah in this case entails the good deed of monotheism as well as the sin of lying, whereas swearing by other than Allah while being truthful entails the good deed of honesty as well as the sin of polytheism. Nevertheless, the reward for monotheism is definitely greater than the reward for honesty, and the sin of lying is undoubtedly less serious than the sin of polytheism.