Is it mentioned in a prophetic Hadith that the formula for responding to a sneezer is "May Allah guide you and rectify your state of affairs," or has this been transmitted by tawatur from the Messenger of Allah, may Allah bless him and grant him peace?

"Yarhamukum Allah" (May Allah have mercy on you) is said to one who sneezes after he has praised Allah. The sneezer then responds with "Yahdikum Allah wa Yuslihu Balakum" (May Allah guide you and rectify your affairs). As for supplicating with "Yahdikum Allah wa Yuslihu Balakum" only, it was mentioned in the context of disbelievers.