«كان إذا عطس حمد الله فيقال له: يرحمك الله فيقول: يهديكم الله ويصلح بالكم»
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 praise Allah, and it would be said to him (peace and blessings be upon him): May Allah have mercy on you. Then he (peace and blessings be upon him) would say: May Allah guide you and set your affairs right."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4754
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[حم طب] عن عبد الله بن جعفر. الصحيحة ٢٣٨٧: طب - ابن عمر.