Listen LiveAbstention
Fasting in Arabic originally means abstention, therefore we should not only abstain from food and drink but from anything that displeases Allāh سبحانه وتعالى. Thus the fast of speech will mean abstention from all foul, offensive and sinful speech which is ḥarām (forbidden). Otherwise, if a person remains hungry and thirsty while continuing to do sinful acts, he/she would not have fulfilled the purpose of fasting.
[This excerpt is based on a majlis (gathering for spiritual training) held by Shaykh Riyadh ul Haq].