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.