Is swearing (by God) forbidden?

The Prophet, peace and blessings be upon him, used to swear to affirm important matters by saying: "By Him in Whose Hand is Muhammad’s soul." Scholars have inferred the permissibility of swearing without being asked to, but one should not do so excessively, especially if the one swearing is not certain of fulfilling his oath, due to the Almighty’s saying: "And guard your oaths." And He censured those who swear excessively in His saying: "And do not obey every [habitual] swearer, a disgrace." As for swearing by other than Allah, it is forbidden and has been explicitly called shirk (polytheism) in hadiths such as: "Whoever swears by other than Allah has committed shirk," and "Indeed, Allah forbids you from swearing by your fathers. Whoever is to swear, let him swear by Allah or remain silent."