What is the authenticity of the the hadith: "Whoever invokes blessings upon me one hundred times every Friday, Allah will forgive him, even if his sins are like the foam of the sea"?

We have not come across the specific wording that the questioner wishes to verify. However, several authentic hadiths have been established regarding the virtue of sending blessings upon the Prophet (peace be upon him), among them:

- His (peace be upon him) saying: "When you hear the Mu'adhdhin, say as he says, then send blessings upon me, for indeed whoever sends blessings upon me once, Allah will send blessings upon him ten times..." (Narrated by Muslim).

- His (peace be upon him) saying: "Whoever sends blessings upon me once, Allah will send blessings upon him ten times" (Narrated by Muslim).

- Regarding the virtue of sending blessings upon him on Friday, he (peace be upon him) said: "Indeed, among your best days is Friday. On it Adam was created, on it he died, on it the trumpet will be blown, and on it the swoon will occur. So, increase your blessings upon me on it, for indeed your blessings are presented to me..." And when he was asked how they would be presented to him when his body had decayed, he replied: "Indeed, Allah Almighty has forbidden the earth to consume the bodies of the Prophets" (Narrated by Abu Dawud and authenticated by Al-Albani).