I say, and with God's success: It is recommended to use siwak when rinsing the mouth or before it; so that one may attain the virtue mentioned in his saying (peace be upon him): “The merit of prayer with siwak over prayer without siwak is seventy times greater,” narrated by Ahmad, Al-Bazzar, Abu Ya'la, Ibn Khuzaymah, and Al-Hakim from Aisha. This virtue is achieved by using it during ablution, so every prayer performed with that ablution has this virtue. And due to his saying (peace be upon him): “If it were not for the hardship it would cause my nation, I would have commanded them to use siwak at every ablution,” in Sahih Bukhari 2: 682.

If one forgets it when rinsing the mouth or before it, then at the time of standing for prayer, some have said: it is recommended in five situations: when the teeth become yellow, when the breath changes, when getting up from sleep, when standing for prayer, and when performing ablution. A rough cloth or a finger can serve as a substitute for siwak when it is unavailable, just as chewing gum can substitute for it in reward for a woman if she is able to do so with the right intention. Refer to: Tabyin al-Haqaiq 1: 4, and Tuhfat al-Nusak on the virtue of siwak p. 47, and Radd al-Muhtar 1: 77, and Al-Hadiyyah al-Alaiyyah p. 24, and Bada'i al-Sana'i, 1: 19, and Al-Ikhtiyar, 1: 12, and Allah knows best.