We have been through this countless times. The Trinity is revealed throughout the OT…beginning in Genesis 1:26. I think it is a rather unusual argument to defend muslim worship on the basis of trying to say that the Trinitarian God was not revealed in the OT.
I will let St Augustine speak to Christ being revealed.
St Augustine**’s reply to Faustus**
You ask me to show what Moses wrote of Christ. Many passages have already been pointed out. But who could point out all? Besides, when any quotation is made, you are ready perversely to try to give the words another meaning;
St Augustine**’s reply to Faustus**
Well, then, O thou full of all subtilty, when the Lord in the Gospel says, “If ye believed Moses, ye would believe me also, for he wrote of me,” there is no occasion for the great perplexity you pretend to be in, or for the alternative of either pronouncing this verse spurious or calling Jesus a liar. The verse is as genuine as its words are true.
St Augustine****
To your own destruction, and to the detriment of the welfare of mankind, you try to weaken the authority of the gospel, by arguing that it cannot be true that Christ said that Moses wrote of Him;
And now the Holy Spirit:
Cast me not away from thy face; and take not thy holy spirit from me.
(Psalm 50:13)
Number 11:26-30
Now there remained in the camp two of the men, of whom one was called Eldad, and the other Medad, upon whom the spirit rested; for they also had been enrolled, but were not gone forth to the tabernacle. And when they prophesied in the camp, there ran a young man, and told Moses, saying: Eldad and Medad prophesy in the camp. Forthwith Josue the son of Nun, the minister of Moses, and chosen out of many, said: My lord Moses forbid them. But he said: Why hast thou emulation for me? O that all the people might prophesy, and that the Lord would give them his spirit! And Moses returned, with the ancients of Israel, into the camp.
Ex 31:1-3
And the Lord spoke to Moses, saying: Behold, I have called by name Beseleel the son of Uri the son of Hur of the tribe of Juda, And I have filled him with the spirit of God, with wisdom and understanding, and knowledge in all manner of work.
Isaiah 63: 7-10
I will remember the tender mercies of the Lord, the praise of the Lord for all the things that the Lord hath bestowed upon us, and for the multitude of his good things to the house of Israel, which he hath given them according to his kindness, and according to the multitude of his mercies. And he said: Surely they are my people, children that will not deny: so he became their saviour. In all their affliction he was not troubled, and the angel of his presence saved them: in his love, and in his mercy he redeemed them, and he carried them and lifted them up all the days of old. But they provoked to wrath, and afflicted the spirit of his Holy One: and he was turned to be their enemy, and he fought against them.
