The Messenger of Allah ﷺ said, "I have been commanded to use the siwak so often that I feared it would be made obligatory upon me."
قال حدثنا إسماعيل قال حدثنا ليث عن أبي بردة عن أبي مليح بن أسامة
قال رسول الله ﷺ أمرت بالسواك حتى خشيت أن يكتب علي
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Its isnad is hasan because of Layth bin Abu Salim. As for Ismail, he is Ibn Ulaya, and Abu Burda is the son of Abu Musa Ashari, and he is trustworthy, among the most excellent. Abu Malih bin Usama bin Umayr Hudhali is likewise trustworthy, among the most excellent. Ibn Majah narrated the hadith, 1/106, no. 289, in the chapter on Purification, on the tooth-stick.