Whenever the Messenger of Allah ﷺ sneezed, he would place his hand or his garment over his mouth and lower or muffle his voice with it. Yahya was uncertain which of the two he said.
حدثنا مسدد حدثنا يحيى عن ابن عجلان عن سمي عن أبي صالح
كان رسول الله ﷺ إذا عطس وضع يده أو ثوبه على فيه وخفض أو غض بها صوته شك يحيى
[Its chain is hasan]. Tirmidhi transmitted it in the Book of Manners, chapter on lowering the voice and covering the face when sneezing, no. 2745, from the hadith of Yahya Qattan, with this wording, and he said, hasan sahih. Al-Hakim graded it sahih (4/293), and Dhahabi agreed with him. Muhammad bin Ajlan explicitly stated that he heard it directly, as recorded by Ahmad (2/439).