Hazrat Mufti Mahmood Hasan Gangohi (rahmatullahi ‘alaihi) said:
The tongue is a great bounty of Allah Ta‘ala. Many good deeds (tilaawat of the Quraan, zikr, tasbeeh and istighfaar etc.) are performed by the tongue and one should occupy the tongue in these good deeds. Using the tongue for filthy purposes like lies, backbiting, carrying tales, slander and swearing etc. is like placing an impure substance on clean clothing. (Malfoozaat of Faqeehul Ummat, vol. 1, pg. 417)