The Prophet ﷺ said, "Respond to the sneezer three times. After that, if you wish to respond again, then do so, and if you wish, refrain."
حدثنا هارون بن عبد الله حدثنا مالك بن إسمعيل حدثنا عبد السلام بن حرب عن يزيد بن عبد الرحمن عن يحيى بن إسحق بن عبد الله بن أبي طلحة
عن النبي ﷺ قال تشمت العاطس ثلاثا فإن شئت أن تشمته فشمته وإن شئت فكف
[Its chain of transmission is daif] Tirmidhi narrated it in the Book of Manners, chapter "How Many Times Should the Sneezer Be Blessed?", no. 2744, from the hadith of Abdul-Salam bin Harb through this route, and he said, gharib (rare), and its chain of transmission is unknown. Yazid Dalani Abu Khalid used ambiguous transmission wording (anana), Ubayda bint Ubayd's condition is not known, and Humaydah was not deemed reliable by anyone except Ibn Hibban.