Mat 26:27 And he took a cup, and when he had given thanks he gave it to them, saying, "Drink of it, all of you, Mat 26:28 for this is my blood of the covenant, which is poured out for many for the forgiveness of sins.
Finally, the Earliest Christians also said any consideration of this as just a metaphor was false
There is no scriptural proof. I've read the church fathers. Some of the things they said were not too impressive. In fairness to them, they were coming from pagan cultures trying to understand the scriptures. You have a lot of Christian Greek fathers saying things that were poorly understood and in which they were viewing doctrine with a pagan understanding. They were more evangelists than teachers.
Catholics tend to pick and choose what early writings they want to believe and which ones they don't. The early fathers also believed our Lord paid the penalty for sin to appease the Father's wrath for us. Heck, they believed that for 1500 years. Do you believe that?
But I'm less impressed with today's Catholics when tell me they're following the early fathers and traditions. They hide behind the magisterial who tells the folks which parts of the early fathers are right and which are wrong. They even change what the fathers originally said and was accepted by saying, "Well, we've come to a deeper understanding."; discarding what was taught. It's no different then the Pharisees, teaching traditions and changing laws and theology so they fit with whatever benefits the "Church" at the time.
So no, I'm not impressed anymore when Catholics quote me the church fathers. It's nothing more than a lie and a game.
Beyond what Christ said according to scriptures, what further "proof" would you need? We know that +Ignatius of Antioch believed in the Real Presence. We know that the 2nd century anaphorae of The Church certainly appear to teach the Real Presence. It is also apparent that there were people running around at the end of the 1st century and into the 2nd who didn't believe in the Real Presence, but that understanding of scripture seems to have faded away until after Luther. In any event, what would scripture have to say to convince you that Christ meant what he said?
"The early fathers also believed our Lord paid the penalty for sin to appease the Father's wrath for us. Heck, they believed that for 1500 years."
The Fathers did, HD? Which ones?