A three-part exchange
Each person has a line, and the third belongs to the one who sneezed.
إِذَا عَطَسَ أَحَدُكُمْ فَلْيَقُلِ الْحَمْدُ لِلَّهِ. وَلْيَقُلْ لَهُ أَخُوهُ أَوْ صَاحِبُهُ يَرْحَمُكَ اللَّهُ. فَإِذَا قَالَ لَهُ يَرْحَمُكَ اللَّهُ. فَلْيَقُلْ يَهْدِيكُمُ اللَّهُ وَيُصْلِحُ بَالَكُمْ
When one of you sneezes let him say: all praise is for Allah. Let his brother say: may Allah have mercy on you. And let him reply: may Allah guide you and set your affairs right.
The full narration
Narrated Abu Huraira:The Prophet (ﷺ) said, " If anyone of you sneezes, he should say 'Al-Hamduli l-lah' (Praise be to Allah), and his (Muslim) brother or companion should say to him, 'Yar-hamuka-l-lah' (May Allah bestow his Mercy on you). When the latter says 'Yar-hamuka-llah", the former should say, 'Yahdikumul-lah wa Yuslih balakum' (May Allah give you guidance and improve your condition)
Source
Ṣaḥīḥ al-Bukhārī · 6224
- Agreed upon as authentic (al-Bukhārī / Muslim)