Mukhtasar Muslim

Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates that two men sneezed in the presence of the Messenger of Allah (peace and blessings be upon him). The Prophet (peace and blessings be upon him) responded to one of them and did not respond to the other. The one to whom he did not respond said, "He sneezed and you responded to him, but I sneezed and you did not respond to me." The Prophet (peace and blessings be upon him) said, "He (i.e., the one to whom I responded) said 'Alhamdulillah,' but you did not say 'Alhamdulillah,' so I did not respond to you."

It is narrated from Iyas bin Salamah that his father (Sayyiduna Salamah bin Akwa’ رضي الله عنه) heard the Noble Prophet صلى الله عليه وسلم, that a man sneezed in the presence of the Prophet صلى الله عليه وسلم, so the Prophet صلى الله عليه وسلم said, "Yarhamuk Allah (may Allah have mercy on you)." Then he sneezed again, so the Prophet صلى الله عليه وسلم said, "He has caught a cold." (That is, if someone is sneezing due to a cold, up to what point should one say "Yarhamuk Allah" to him?)