Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Abu Burdah (may Allah be pleased with him), he says: I went to Sayyiduna Abu Musa (may Allah be pleased with him), he was in the house of the daughter of Umm al-Fadl. When I sneezed, Abu Musa did not supplicate for me by saying «يرحَمك الله», but when the daughter of Umm al-Fadl sneezed, he gave her a supplicatory response. I went back and told my mother the whole matter. When Abu Musa came to my mother, she asked: When my son sneezed, why did you not say «يرحمك الله» and when so-and-so sneezed, you supplicated for her? (What is the reason for this difference?) He said: Your son did sneeze, but he did not say «اَلْحَمْدُ لِلّٰهِ», so I did not say the supplicatory words, and the daughter of Umm al-Fadl sneezed and said «اَلْحَمْدُ لِلّٰهِ», so I said «يرحَمك الله», and I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "When someone sneezes and says «اَلْحَمْدُ لِلّٰهِ», then you should supplicate for him (by saying «يرحَمك الله»), and if he does not say «اَلْحَمْدُ لِلّٰهِ», then you should not supplicate for him." (Upon hearing this hadith) she said: You did well, very well.

It is narrated from Sayyiduna Abdullah bin Ja'far Dhuljanahain (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) sneezed, he would say «اَلْحَمْدُ لِلّٰهِ». Then when «يرحَمك الله» was said in response, the Prophet (peace and blessings be upon him) would say: "«يهديكم الله و يصلح بالكم» May Allah guide you and rectify your condition."