It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: "When one of you yawns, he should try to restrain it as much as possible."
Hadith Referenceالادب المفرد / كتاب العطاس والتثاؤب / 942
Hadith Gradingالألبانی:صحيح
Hadith Takhrij«صحيح : صحيح مسلم ، الزهد و الرقائق ، ح : 2994 و أحمد : 397/2»