What is Jerome's "Hebrew" Gospel?

[trettep]

The following is a quote from Jerome, Against the Pelagians, Book III, located here:

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2. In the Gospel according to the Hebrews, which is written in the Chaldee and Syrian language, but in Hebrew characters, and is used by the Nazarenes to this day (I mean the Gospel according to the Apostles, or, as is generally maintained, the Gospel according to Matthew, a copy of which is in the library at Caesarea), we find, "Behold, the mother of our Lord and His brethren said to Him, John Baptist baptizes for the remission of sins; let us go and be baptized by him. But He said to them, what sin have I committed that I should go and be baptized by him? Unless, haply, the very words which I have said are only ignorance." And in the same volume, "If thy brother sin against thee in word, and make amends to thee, receive him seven times in a day." Simon, His disciple, said to Him, "Seven times in a day?" The Lord answered and said to him, "I say unto thee until seventy times seven."

Looking at the underlined portion, I have been unable to locate the source for this quote in the Peshitta or in any of the Hebrew versions of Matthew. From which source is Jerome quoting? Is this from the Diatesseron?

In Messiah,
Wayne

The underlined section makes sense to me. For John's baptism was one of repentance which means to turn and walk in the opposite direction. Jesus was already in the right direction and wasn't sinning. Jesus already has the Holy Spirit otherwise He could never have known God and like his cousin John both had it from birth. Jesus actually had it long before being born as a man. But Jesus had to be baptized not for forgiveness of sins or to receive the Holy Spirit but to set an example of instruction in righteousness. John's baptism was a type of the later Holy Spirit baptism.

Paul