The person who responds to someone's sneeze should say, Yarhamukallah. Then the sneezer will say again -
يَرْحَمُنَا اللَّهُ وَإِيَّاكُمْ، وَيَغْفِرُ لَنَا وَلَكُمْ
Pronunciation
yar'hamunallahu wa iyyakum wa yaghfiru lanaa walakum
Meaning
May Allah shower his mercy upon you and us and forgive you and us.
Source: Adabul Mufrad: 941
Read the hadith
"حَدَّثَنَا فَرْوَةُ، وَأَحْمَدُ بْنُ إِشْكَابَ، قَالاَ: حَدَّثَنَا الْقَاسِمُ بْنُ مَالِكٍ الْمُزَنِيُّ، عَنْ عَاصِمِ بْنِ كُلَيْبٍ، عَنْ أَبِي بُرْدَةَ قَالَ: دَخَلْتُ عَلَى أَبِي مُوسَى، وَهُوَ فِي بَيْتِ ابْنَتِهِ أُمِّ الْفَضْلِ بْنِ الْعَبَّاسِ، فَعَطَسْتُ فَلَمْ يُشَمِّتْنِي، وَعَطَسَتْ فَشَمَّتَهَا، فَأَخْبَرْتُ أُمِّي، فَلَمَّا أَتَاهَا وَقَعَتْ بِهِ وَقَالَتْ: عَطَسَ ابْنِي فَلَمْ تُشَمِّتْهُ، وَعَطَسَتْ فَشَمَّتَّهَا، فَقَالَ لَهَا: إِنِّي سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ: إِذَا عَطَسَ أَحَدُكُمْ فَحَمِدَ اللَّهَ فَشَمِّتُوهُ، وَإِنْ لَمْ يَحْمَدِ اللَّهَ فَلاَ تُشَمِّتُوهُ، وَإِنَّ ابْنَكِ عَطَسَ فَلَمْ يَحْمَدِ اللَّهَ، فَلَمْ أُشَمِّتْهُ، وَعَطَسَتْ فَحَمِدَتِ اللَّهَ فَشَمَّتُّهَا، فَقَالَتْ: أَحْسَنْتَ.
Abu Burda said, ""I came to Abu Musa while he was in the house of Umm al-Fadl ibn al-'Abbas and I sneezed and Abu Musa did not wish mercy on me. Umm al-Fadl sneezed and he wished mercy on her. I told my mother, so when Abu Musa came to her, she confronted him and said, 'My son sneezed and you did not wish mercy on him. She (Umm al-Fadl) sneezed and you wished mercy on her.' Abu Musa replied, 'I heard the Prophet, may Allah bless him and grant him peace, say, ""When one of you sneezes and praises Allah, you should wish mercy on him, if he does not praise Allah, do not wish mercy on him."" My son sneezed and did not praise Allah, so I did not wish mercy on him. She sneezed and praised Allah, so I wished mercy on her.' She said, 'You did well.'"" [Adabul Mufrad: 941]
Duas from IslamicAPI's Masnun Dua dataset (based on the Quran, hadith, Hisnul Muslim and Rahe Belayat). See the dataset