وَعَن أبي أَيُّوب أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: إِذا عطسَ أحدكُم فلْيقلْ: الحمدُ لله عَلَى كُلِّ حَالٍ وَلْيَقُلِ الَّذِي يَرُدُّ عَلَيْهِ: يَرْحَمك الله وَليقل هُوَ: يهديكم وَيصْلح بالكم رَوَاهُ التِّرْمِذِيّ والدارمي
It is narrated from Abu Ayyub (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you sneezes, he should say: All praise is due to Allah in every circumstance. And whoever responds to him should say: May Allah have mercy on you. And he (the one who sneezed) should say: May Allah guide you and rectify your condition." Its chain is weak. Narrated by al-Tirmidhi and al-Darimi.