Muwatta Malik, Book 54, Hadith 1769 (In-Book)

Malik related to me from Abdullah ibn Abi Bakr from his father that the Messenger of Allah, may Allah bless him and grant him peace, said, "If a man sneezes, invoke a blessing on him. Then if he sneezes, invoke a blessing on him. Then if he sneezes, invoke a blessing on him. Then if he sneezes, say, 'You have a cold'." Abdullah ibn Abi Bakr said, "I don't know whether it was after the third or fourth."

حَدَّثَنِي مَالِكٌ، عَنْ عَبْدِ اللَّهِ بْنِ أَبِي بَكْرٍ، عَنْ أَبِيهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ إِنْ عَطَسَ فَشَمِّتْهُ ثُمَّ إِنْ عَطَسَ فَشَمِّتْهُ ثُمَّ إِنْ عَطَسَ فَشَمِّتْهُ ثُمَّ إِنْ عَطَسَ فَقُلْ إِنَّكَ مَضْنُوكٌ ‏" ‏ ‏.‏ قَالَ عَبْدُ اللَّهِ بْنُ أَبِي بَكْرٍ لاَ أَدْرِي أَبَعْدَ الثَّالِثَةِ أَوِ الرَّابِعَةِ

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also referenced under: Book 54, Hadith 4 (USC-MSA)