What is the ruling on using the siwak?

The siwak is generally recommended under all circumstances. This is based on the hadith reported by ʿAisha (may Allah be pleased with her) from the Messenger of Allah (peace and blessings be upon him) who said, “The siwak is a purification for the mouth and pleasing to the Lord” (recorded by Bukhari in a suspended (muʿallaq) chain of transmission, and by Ibn Majah and al-Nasaʾi). Abu Huraira (may Allah be pleased with him) narrated that the Messenger of Allah (peace and blessings be upon him) said, “Were it not for the hardship this would cause my community, I would have commanded them to use the siwak at every prayer” (recorded by Bukhari and Muslim).

Using the siwak is even more strongly recommended in five circumstances: when rising for prayer, when the teeth become yellow, when performing ablution, when reciting the Quran, and when the mouth’s odor or condition changes. Such changes may result from sleep, eating foods with an unpleasant odor, abstaining from food and drink, prolonged silence, or excessive speech.

And Allah Almighty knows best.