I didn't say anything about "instructions"; I said Law.
However, here are several examples:
Abel, Genesis 4:4
Abraham, Genesis 15:6
Naaman, 2 Kings 5:17-19
Etc.
The word "Torah" means "instruction", though it is commonly translated as "law" insofar as laws are instructions that we are obligated to follow.
In Genesis 4:7, God told Cain that sin was crouching at the door and that he must master it, which implies that he already knew what sin is and must have already been given instructions in that regard. It is not directly recorded that God instructed them to make offerings, but it is clear that Abel knew how to make an acceptable offering and must have already been given instructions in that regard, which Cain did not follow.
In Psalms 119:29, he wanted to put false ways far from him, for God to be gracious to him by teaching him to obey the Torah, and he chose the way of faithfulness by setting it before him, so this has always been the one and only way of salvation by grace through faith. In Exodus 33:13, Moses wanted God to be gracious to him by teaching him to walk in His way that he might know Him and Israel too. In Genesis 6:8-9, Noah found grace in the eyes of God, he was a righteous man, and he walked with God, so God was gracious to him by teaching him to walk in his way in obedience to the Torah and he was righteous because he obeyed through faith. Moreover, in Genesis 7:2, Noah was told what to do with clean and unclean animals without being told how to tell the difference, and in 8:20, he knew to offer a clean animal, so he must have already been given instructions in that regard.
In Matthew 4:15-23, Jesus began his ministry with the Gospel message to repent for the Kingdom of God is at hand, which was a light to the Gentiles, and the Torah is how his audience knew what sin is (Romans 3:20), so repenting from our disobedience to it is a central part of the Gospel message, which is in accordance with Jesus being sent in fulfillment of the promise to bless us by turning us from our wickedness (Acts 3:25-26), which is the Gospel that was made known in advance to Abraham in accordance with the promise (Galatians 3:8), which he taught to Gentiles in Haran in accordance with the promise (Genesis 12:1-5). So God was gracious to Abraham by teaching him to walk in His way in obedience to His commandment, statutes, and laws in accordance with the promise (Genesis 26:4-5).
So it is clear that God has given instructions even when it is not directly stated when He gave them.
With respect, you're missing the point. First, one does not "have faith" in instructions; one "has faith" in God.
It is contradictory to have faith in God, but not in His instructions. If I were lost and asked someone for directions, but by following exactly what they instructed I would be putting by faith in them to correctly guide me. There are many verses that connect our faith in God with our obedience to His instructions, such as in Matthew 23:23, Jesus said that faith is one of the weightier matters of the Torah. In James 2:18, he would show his faith by his works. in Romans 1:5, we have received grace in order to bring about the obedience of faith. In Revelation 14:12, those who kept faith in Jesus are the same as those who kept God's commandments. In John 3:36, obeying Jesus is equated with believing in him. In Numbers 5:6, disobedience to the Torah is referred to as breaking faith. In Hebrews 3:18-19, it equates their disobedience with their unbelief. The way to have faith in God's goodness as the guide for how to rightly live our lives is by following His instructions for how to testify about His goodness.