From al-Malfūdh Sharīf, Pg 302,

Question

Is it permissible to fold one’s beard? [I.e. push it under one’s chin]

Answer

It is stated in Hadith Sharif: He who folds [or ties] their beards, let it be known that [the Beloved Messenger] Muhammad is disgusted with them.[1] 

[1] Fath al-Bārī cited from Sunan Abu Dāwud