The Prophet ﷺ said: Invoke a blessing on one who sneezes three times; (and if he sneezes more often), then if you wish to invoke a blessing on him, you may invoke, and if you wish (to stop), then stop.
عَنِ النَّبِيِّ ﷺ قَالَ تُشَمِّتُ الْعَاطِسَ ثَلاَثًا فَإِنْ شِئْتَ أَنْ تُشَمِّتَهُ فَشَمِّتْهُ وَإِنْ شِئْتَ فَكُفَّ
from his mother, from her father, who said: "The Messenger of Allah ﷺ said: 'Reply three times to the sneezing person. If he (sneezes) more, then if you wish reply and if you do not then do not.'"
قَالَ رَسُولُ اللَّهِ ﷺ يُشَمَّتُ الْعَاطِسُ ثَلاَثًا فَإِنْ زَادَ فَإِنْ شِئْتَ فَشَمِّتْهُ وَإِنْ شِئْتَ فَلاَ
"يُشَمَّتُ الْعَاطِسُ ثَلَاثًا، فَإِنْ زَادَ فَإِنْ شِئْتَ فَشَمِّتْهُ وَإِنْ شِئْتَ فَكُفَّ".
"شَمِّتِ الْعَاطِسَ ثَلَاثًا؛ فَإِنْ زَاد فَإِنْ شِئْتَ فَشَمِّته وإن شئت فلا"