What should the fasting person do and what is obligatory upon him?
The fasting person should increase in the acts of obedience (to Allah) and avoid all of the prohibitions. It is obligatory upon him to guard the performance of the obligatory acts and stay away from the forbidden things. Thus, he should pray the five prayers in their times with the congregation, He should abandon lying, backbiting, cheating and treachery, interest and usury based dealings, and every statement or action that is forbidden . The Prophet-Sallallahu alaihi wasallam- said: Whoever does not abandon false speech, acting according to it and ignorance, then Allah has no need of him abandoning his food and drink
1. Al-Bukhari no 1903
Shaykh Muhammad bin Saalih al-`Uthaymeen
Fatawa Islamiyah Page no. 244 Vol: 2