Is there any scripture that indicates that anyone before the law was given through Moses observed Sabbath ritual?
Well, before Mose time there were something people did, such as offering to the Lord, which where being done, on the High, and Holy Sabbath days, which could be consider ritual as you call it.
Remember Cain and abel...In Genesis 4: 1 And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the LORD. 2 And she again bare his brother Abel. And Abel was a keeper of sheep, but Cain was a tiller of the ground. 3 And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the LORD. 4 And Abel, he also brought of the firstlings of his flock and of the fat thereof. And the LORD had respect unto Abel and to his offering: 5 But unto Cain and to his offering he had not respect.
So we have offering to the Lord which was still past down to the generations.
In Genesis 8:20 - And Noah builded an altar unto the LORD; and took of every clean beast, and of every clean fowl, and offered burnt offerings on the altar.
We also have Abraham, when offer his son Issac. Genesis 22:2 - And he said, Take now thy son, thine only son Isaac, whom thou lovest, and get thee into the land of Moriah; and offer him there for a burnt offering upon one of the mountains which I will tell thee of.
Genesis 22:3 - And Abraham rose up early in the morning, and saddled his ***, and took two of his young men with him, and Isaac his son, and clave the wood for the burnt offering, and rose up, and went unto the place of which God had told him.
Genesis 22:8 - And Abraham said, My son, God will provide himself a lamb for a burnt offering: so they went both of them together
In Genesis 35:14 - And Jacob set up a pillar in the place where he talked with him, even a pillar of stone: and he poured a drink offering thereon, and he poured oil thereon.
And of Course we have Moses in Exodus 10:25 - And Moses said, Thou must give us also sacrifices and burnt offerings, that we may sacrifice unto the LORD our God.