When a disbeliever praises Allah after sneezing1 du'a

May Allah guide you and set your affairs in order

Reference:At-Tirmidhi 5/82, Ahmad 4/400, Abu Dawud 4/ 308. See also Al-Albani, Sahih At-Tirmidhi 2/354.Hisnul Muslim 189

يَهْـديكُـمُ اللهُ وَيُصْـلِحُ بالَـكُم

Transliteration

Yahdīkumullāhu wa yuṣliḥu bālakum.

Translation

May Allah guide you and set your affairs in order