Your Companion Should Reply

يَرْحَمُكَ اللهُ
Translation: May Allah have mercy on you.
Transliteration: Yarḥamuka-llāh.
Virtue: The Messenger of Allah ﷺ said, “If anyone of you sneezes, he should say ‘Al-ḥamdu li-llāh’ (Praise be to Allah), and his (Muslim) brother or companion should say to him, [the above]. (Bukhārī 6224)