that the Messenger of Allah (ﷺ) said: "The sneeze is from Allah and the yawn is from Ash-Shaitan. So when one of you yawns let him cover his mouth with his hand. For when he says 'Ah, Ah' Ash-Shaitan laughs from inside his opening."
Jami` at-Tirmidhi Book 43, Hadith 16
← Previous Hadith that when the Prophet (ﷺ) would sneeze, he would cover his face with his hand or with his garment, and muffle the sound with it.

Jami` at-Tirmidhi Book 43, Hadith 15 Next Hadith → that the Messenger of Allah (ﷺ) said: "Indeed Allah loves sneezing and He dislikes the yawn. So when one of you sneezes and says 'Al-Hamdulillah (All praise is due to Allah),' then it is a right due from every one who hears him to say: 'Yarhamukallah (May Allah have mercy upon you)' As for yawning then when one of you yawns let him suppress it as much as possible and not say: "Hah Hah' for that is only from Ash-Shaitan laughing at him."

Jami` at-Tirmidhi Book 43, Hadith 17