Imam Aḥmad reports, on the authority of Ruwayfiʿ—may Allah be pleased with him—that the Messenger of Allah ﷺ said to him: “O Ruwayfiʿ, you may live a long life after me, so inform the people that whoever knots his beard, hangs a string as a talisman, or performs istinjāʾ (removes excrement) with the dung of an animal or with a bone—then Muhammad disowns him.”(1)
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Ruwayfiʿ: Ruwayfiʿ ibn Thābit ibn al-Sakan ibn ʿAdī ibn al-Ḥārith, of the clan of Mālik ibn al-Najjār from the Anṣār. He governed Barqah and Tripoli, opened Ifriqiyyah in 47 AH, and died in Barqah in 56 AH.

“Knots his beard”: Some say this refers to what warriors used to do in battle—twisting and tying the beard out of pride. Others say it means treating the hair so that it becomes matted and curled in an effeminate, self-indulgent manner. A third view is that it denotes knotting or clutching it during prayer.

“Hang a string”: placing it as a necklace on one’s own neck or on the neck of an animal to ward off the evil eye.

“Istinjāʾ”: removing najw (excrement) from the outlet.

“Animal dung”: dung is called rajīʿ (“that which has returned”) because it reverts to a new form after first being fodder.

“Disowns him”: a severe threat directed at anyone who commits such acts.

Overall purport of the ḥadith: the Prophet ﷺ tells this Companion that he will live long enough to encounter people who violate the Prophetic practice concerning beards, whose sunnah is to let them grow