Musnad Ahmad 1060:60

Muhammad ibn Ja'far and Hajjaj narrated to us, they said: Shu'bah narrated to us, from Muhammad ibn Abi Layla, from his brother 'Isa, from his father, from Abu Ayyub, from the Prophet, peace and blessings of Allah be upon him, that he said: "When one of you sneezes, let him say: 'Praise be to Allah in every state.' And let the one who responds to him say: 'May Allah have mercy on you (Yarhamuk Allah).' And let him [the one who sneezed] say: 'May Allah guide you and rectify your state (Yahdika Allah wa yuslihu balak).'" Hajjaj said: "May Allah guide you all and rectify your state (Yahdikum Allah wa yuslihu balakum)."