Some Messianic prophecies occur near the beginning of the Bible, such as Deuteronomy 18:15 (or even Genesis 3:15). What I want to understand is which Messianic prophecy do scholars believe was actually recorded first?
Does, for example, the Immanuel prophecy of Isaiah 8:23-9:1 predate Deuteronomy 18?
If that question is too difficult, due to questions of authorship and redaction, can we ask
What is the earliest date for which historians are confident Messianic prophecy existed in Israel?
The first Messianic prophecy occurs in the first book of the Bible, Genesis 3:15., probably written in the 15th century BC. We can't readily distinguish the chronology between the 5 books of the Pentateuch (Genesis, Exodus, Leviticus, Numbers, Deuteronomy), but they were among the first books of the OT to be written. Job is actually normally considered the earliest written book of the Bible, with an unknown date but with a proposed Messianic prophecy in Job 19:25 "I know that my Redeemer lives", described in this article. Besides Job, Genesis is seemingly the first to be penned.
Genesis 3:15 "And I will put enmity between you and the woman, and between your offspring and hers; he will crush your head, and you will strike his heel.”"
The significance of the verse (explained by Blue Letter Bible and Ligonier Ministries) is that the He is referring to Jesus and we know this because "he" is singular in Hebrew, even though the previous statement refers to the plural "offspring." A "surprisingly" similar verse in the New Testament is
Romans 16:20 "And the God of peace will crush Satan under your feet shortly."
It is likely that the "striking his heel" refers to Jesus' crucifixion, and the final crushing will occur at His Second Coming when He, holding the keys of death and Hades, will lock up and deal with Satan completely. The onset of the Kingdom of God also relates to Jesus "binding the strong man" (Mark 3:27).
So the prophecy is that a single, particular offspring (Jesus) will crush Satan, and Satan will strike his heel, corresponding to Jesus' crucifixion and 2nd Coming. This prophecy was likely recorded in written form (though passed down for generations accurately through oral transmission in an oral culture) around 1445-1405 BC. (The link is not an academic source; I have just seen that date range for the Pentateuch from multiple sources repeatedly).
Again, Job is proposed to be written earlier (unknown date) with a prophecy in Job 19:25 "I know my Redeemer lives." See this article.
In Genesis 15:12, God promises Abraham an exile and a redemption, though God does not specify any particular human figure effecting the redemption. A Messianic prophecy, without a Messiah.
12 As the sun was setting, Abram fell into a deep sleep, and a thick and dreadful darkness came over him. 13 Then the Lord said to him, “Know for certain that for four hundred years your descendants will be strangers in a country not their own and that they will be enslaved and mistreated there. 14 But I will punish the nation they serve as slaves, and afterward they will come out with great possessions. 15 You, however, will go to your ancestors in peace and be buried at a good old age. 16 In the fourth generation your descendants will come back here, for the sin of the Amorites has not yet reached its full measure.”
I would agree that Genesis 3:15 is the first Messianic prophesy. I have a different idea about what crushing the head of the serpent refers to. If you characterize the Satan as a serpent, knowing that the serpent's poison is in his head. Sin being the poison, when Jesus conquered sin you could conclude that the serpent's head has been crushed. There is a more direct reference to a head being crushed, however.
Revelation 17:9 Here is the mind which has wisdom. The seven heads are seven mountains on which the woman sits, 10 and they are seven kings: five have fallen, one is, the other has not yet come; and when he comes, he must remain a little while, 11 And the beast which was and is not, is himself also an eighth, and is of the seven, and he goes to destruction.
The beast is the eighth head. He is of the seven. I take that to mean that he is a descendant of the other seven. Here we have all seven kings embodied in one person, the beast. By destroying the one, he destroys them all.
This is the head that will be crushed by the seed, Jesus, whose heal was bruised on the cross.
