«كان إذا عطس وضع يده أو ثوبه على فيه وخفض بها صوته»
It was the practice of the Prophet (peace and blessings be upon him):
"When he (peace and blessings be upon him) sneezed, he (peace and blessings be upon him) would place his hand or his garment over his mouth and lower his voice."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4755