Using the siwak does not affect the fast; rather, it is recommended and encouraged for both the fasting person and anyone else, at the beginning of the day and at its end, according to the soundest opinion.

If dust or even a fly should enter his throat unintentionally, that does not harm his fast.

The fasting person is obliged to avoid lying, backbiting, and insulting others. If someone abuses or reviles him, he should respond, “I am fasting,” for some people find it easy to leave off food and drink yet find it difficult to abandon the foul words and deeds to which they are accustomed. One of the early generations therefore remarked, “The easiest part of fasting is giving up food and drink.”

Accordingly, the Muslim must be conscious of Allah, fear Him, and remain aware of his Lord’s greatness and His watch over him at all times and in every situation, safeguarding his fast from anything that would invalidate or diminish it so that his fast will be sound.

The fasting person should occupy himself with the remembrance of Allah, the recitation of the Quran, and abundant supererogatory acts of worship. The early generations, when they fasted, would sit in the mosques and say, “We are protecting our fast and will not backbite anyone.” The Prophet ﷺ said, “Whoever does not abandon false speech and acting upon it, Allah has no need for him to abandon his food and drink.” One only truly draws near to Allah by leaving these lawful desires—normally permitted outside of fasting—after first drawing near to Him by forsaking what He has forbidden at all times: lying, oppression, and aggression against people in their lives, property, and honor.

It is narrated from Abu Hurayrah, traced back to the Prophet ﷺ: “The fasting person remains in a state of worship as long as he does not backbite a Muslim…”