Who was Uwais al-Qarni?
Uwais al-Qarni was a man from Yemen who embraced Islam in the lifetime of the Prophet (peace and blessings be upon him), but was not able to come to Medina to visit him since he was in the service of his aging mother. Thus, although he never became a Companion (Sahabi), his status was such that the Prophet (peace be upon him) instructed his Companions that,
“A man called Uwais will come to you from Yemen… whoever amongst you is able to meet him [Uwais], then ask him to pray for your forgiveness,” and that, “Indeed, the best of the Followers [after the generation of my Companions] is a man named Uwais…” [Muslim]
Did Uwais al-Qarni Break His Teeth Out of Grief?
The story in question about Uwais breaking all his teeth because he had heard that the Prophet’s (peace and blessings be upon him) blessed molar tooth was broken at the Battle of Uhud is mentioned in Seerah al-Halabiyyah.
Seerah al-Halabiyyah quotes Imam al-Sha’rani’s Tabaqat al-Kubra, where Imam al-Sha’rani says:
“And it has been narrated… that [Uwais al-Qarni] said, ‘By Allah, the Prophet’s molar tooth (peace and blessings be upon him) was not broken except that I broke my own molar tooth,’… this is how I have seen this quote written in some books, and Allah knows best as to its condition [whether it is authentic or not].” [al-Halabi, Insan al-‘Uyoon aka. Al-Seerah al-Halabiyya]
Hence, it is clear from the quote that the book was not trying to report this tale as a fact, and had a clear doubt as to its authenticity.
I have not been able to find a source from the hadith or seerah books to support this account. I only found that a similar story was reported in Fariduddin ‘Attar’s Tadhikra al-Awliya under Uwais al-Qarni’s biography, without the mention of any source.
Mulla ‘Ali al-Qari settled the question in his short treatise on the virtues of Uwais al-Qarni. He says about this story:
“And know well that that which has become widespread on the tongues of the laity that Uwais [al-Qarni] extracted all his teeth out of extreme grief when he heard that the tooth of the Prophet [Allah’s peace and blessings be upon him] had been struck, [because] he didn’t reliably know which tooth it was exactly – then there is no basis for this [story] according to the scholars…
… along with the fact that it violates the noble Sacred Law, and because of this reason, not one of the Senior Companions did that [act of self-inflicted harm], because this type of act is vain and futile, and not proceeding from anyone except fools.” [‘Ali al-Qari, al-Ma’din al-Adni fi Fadl Uwais al-Qarni]
And Allah Most High knows best.