Is swearing by "Wallahi" permissible or forbidden?

Swearing is prescribed by Allah, Glorified and Exalted be He, and by His Names and Attributes. It is not permissible to swear by other than Allah from His creation, due to the saying of the Messenger of Allah, peace and blessings be upon him: "Indeed, Allah forbids you from swearing by your fathers. Whoever swears, let him swear by Allah or remain silent." It is permissible to swear by saying "واللهِ" (wa-llāhi) with a thickened lām and a kasrah on the hā’. It is not permissible to pronounce the lām with a thin sound and to prolong the kasrah until a yā’ is produced, as this changes both the pronunciation and the meaning.