The Messenger of Allah ﷺ forbade a man from covering his mouth during the prayer.
حدثنا أبو سعيد سفيان بن زياد المؤدب حدثنا محمد بن راشد عن الحسن بن ذكوان عن عطاء
نهى رسول الله ﷺ أن يغطي الرجل فاه في الصلاة
[Its chain is daif] Abu Dawud narrated it in the book of Prayer, in the chapter on letting the garment hang loose during prayer, hadith no. 643, from the hadith of Hasan bin Zakwan, from Sulayman al-Ahwal, from Ataa, with this wording. This Hasan used to practice tadlis, narrating from Amr bin Khalid Wasiti, who was a liar, as stated in Tahdheeb and elsewhere, and elsewhere. So his tadlis is the worst kind of tadlis, and he narrated using the ambiguous form "an."Alqama bin Amr Darimi told us,