I was sitting with the Messenger of Allah ﷺ when a man sneezed. The Messenger of Allah ﷺ said, "May Allah have mercy on you." Then the man sneezed again, and the Messenger of Allah ﷺ said, "The man has a cold."
قال حدثنا بهز عن عكرمة بن عمار قال
كنت قاعدا عند رسول الله ﷺ فعطس رجل فقال رسول الله ﷺ يرحمك الله ثم عطس أخرى فقال رسول الله ﷺ الرجل مزكوم
Its chain of transmission is sahih. The hadith was narrated by Muslim, 4/2292, no. 2993, in the Book of Asceticism, chapter on invoking mercy for the sneezer, by Abu Dawud, 4/308, no. 5037, in the Book of Manners, chapter on how many times one should invoke mercy for the sneezer, and by Darimi, 2/369, no. 2661, in the Book of Seeking Permission, with similar wording. Tirmidhi narrated something similar, 5/84, no. 2743, in the Book of Manners, with similar wording, and said, hasan sahih.