Hold back a yawn as much as you can. The Prophet ﷺ said: “Yawning is from Shayṭān; when one of you yawns, let him restrain it as much as he can, for if he says ‘Haa,’ Shayṭān laughs.” (al-Bukhārī). And: “When one of you yawns, let him put his hand over his mouth, for Shayṭān enters.” (Muslim).
العربية: عن أبي هريرة رضي الله عنه أنّ النبيّ ﷺ قال: «التثاؤب من الشيطان، فإذا تثاءب أحدكم فليردّه ما استطاع». (البخاري). وقال: «فليضع يده على فيه». (مسلم).
When you yawn, restrain it and cover your mouth with your hand.