There are particular occasions when the siwak is especially urged, even though, in principle, it remains a recommended Sunnah at every time. Among the most emphasized moments is upon waking from sleep. It is Sunnah for a person to use the siwak then, because of the report of Hudhayfah (may Allah be pleased with him) that whenever the Prophet (peace and blessings be upon him) rose during the night he would scrub his mouth with the siwak—that is, he would use it. A corroborating narration from ʿĀʾishah (may Allah be pleased with her) states that they used to set out his siwak and water for ablution; when he got up he would use the siwak, perform wuḍūʾ, and pray as much as Allah willed. Hence, whether one wakes by night or by day—since the mouth changes during sleep—it is recommended to use the siwak.
It is likewise recommended to use the siwak the moment one enters his home, for ʿĀʾishah was asked, “What was the first thing the Messenger of Allah (peace and blessings be upon him) would do when he came into his house?” She replied, “He would use the siwak.”
Third: the siwak is recommended when one is about to perform prayer—be it an obligatory prayer, a voluntary prayer involving bowing and prostration, or even the funeral prayer. This is based on the Prophet’s saying (peace and blessings be upon him), “Were it not that I would place a burden on my community, I would have commanded them to use the siwak at every prayer.”
The siwak is also emphatically recommended at the time of wuḍūʾ. Its proper place is while rinsing the mouth, although using it immediately before or after does not nullify the Sunnah. The practice comes from the Prophet (peace and blessings be upon him) himself.
The scholars have added that whenever the mouth changes because of eating, drinking milk, or anything oily, one should use the siwak, for it purifies the mouth. In sum, the siwak is Sunnah at all times, with special emphasis on the occasions mentioned. It remains legislated at every hour—even for the fasting person after the sun has passed its zenith; like everyone else, he is encouraged to use it. Those scholars who considered it disliked at that time have no evidence for their view. The correct opinion is that the fasting person may use the siwak at the start of the day as well. Allah alone grants success.