ENOfficial
Nafi' said that when 'Abdullah ibn 'Umar sneezed, they said to him, "May Allah have mercy on you," and Ibn 'Umar said, "May He have mercy on us and you. May He forgive us and you."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا إِسْمَاعِيلُ، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللهِ بْنِ عُمَرَ، أَنَّهُ كَانَ إِذَا عَطَسَ فَقِيلَ لَهُ: يَرْحَمُكَ اللَّهُ، فَقَالَ: يَرْحَمُنَا اللَّهُ وَإِيَّاكُمْ، وَيَغْفِرُ لَنَا وَلَكُمْ.
sunnah.com