A question about Faith and Law before Sinai William Huntington (1745 – 1813) preached in London to many hundreds, sometimes thousands, in the latter part of his life. After his death a number of preachers followed in his footsteps, such as William Gadsby, John Kershaw, William Tiptaft and, notably, J C Philpot. The movement changed its name in order to separate from what was considered erroneous and in order to define what was seen to be true and the names ‘Strict Baptist’ then ‘Gospel Standard Strict Baptist’ were applied.
Huntington, and those who followed, denied that the Christian was under law (whether ‘moral’ or ‘ceremonial’) and he advanced a variety of texts to support this : I am crucified with Christ, Galatians 2:20 ; Christ is the end of the law for righteousness to everyone that believeth, Romans 10:4 ; ye also are become dead to the law by the body of Christ, Romans 7:4.
Aside from these texts (which are not the subject of this question) Huntington also argued with regard to Old Testament believers - who lived before Moses' delivery of the law, and before the enunciating of the ten commandments to Israel at Sinai.
If no law had yet been delivered, he argues, how then did these saints live ? Such as Abel, Enoch, Noah, Job, Abraham, Isaac, Jacob and Joseph ? They are specifically said to be justified and accounted righteous in the sight of God, but how did they live, thereafter, without law to guide them ?
In his book Law and Grace Contrasted Huntington says :

By faith Enoch had this testimony that he pleased God, Hebrews 11:5 ; but without faith it is impossible to please him, Hebrews 11:6. Then faith is a rule that God approves of, and is pleased with. If the ten commandments be the believer’s only rule of a righteous life, what then of Abel who obtained witness that he was righteous, God testifying of his gifts, Hebrews 11:4, an entire dispensation before the commandments were given ?
Noah, who became heir of the righteousness of faith, Hebrews 11:7, was certainly without the legal rule of works, when he prepared an ark and condemned the world, by faith, without a law to guide him.
Abraham, the friend of God and the father of the faithful and heir of the world must also walk uncertainly [if only law could truly guide him (edit)].

I think it is important to notice that Mr Huntington is not arguing about justification by faith (and how it is achieved), he is arguing regarding a sanctified life, thereafter.
This argument, regarding saints who died before the law was laid down, is that which engages me and I would be interested to know what Protestants have made of it.
I am aware that some Protestants have not accepted what Mr Huntington preached and indeed many have called him, inaccurately, an ‘Antinomian’.
But what do they make of this argument regarding Old Testament saints ?
"saints who died before the law was laid down" is the key issue with this question.  Does "laid down" mean first created, or formalized in writing.

I know you asked for a Protestant position, but it's good to know what people believed before that too.

In particular, Commandments/Laws followed by Avraham - Mi Yodeya, in the Judaism SE site indicates that Jews believe the Law existed in oral form long before it was put into writing by Moses.  This possibly includes even the holy days and feasts such as Passover (long before the actual Passover event).

Chabad.org, How Did the Torah Exist Before it Happened? - Questions &amp; Answers, says:


  This is discussed in many places in Talmud and Midrash. Not only Abraham, Isaac and Jacob, but also Noah and even Adam knew the Torah. Concerning Noah, the Torah itself writes clearly that G‑d told him to take onto his ark "of the animal which is ritually pure (tahor), seven, seven." Apparently, he was expected to know for himself that pigs are not ritually pure and cows are.
  
  What was the Torah before it was given to us? The Torah is G‑d's wisdom, as He considers Himself, as He considers us and as He considers His world. It contains the wisdom with which He creates the world and manages it. Think of a concept paper that a producer might write before developing a video game or some other such product. The Torah contains exactly that (and much more1). Each of the lofty souls we mentioned was able to attain insight into this wisdom and thereby know the hiddenmost secrets of the universe.


As for "Protestants" that's a large category, with many conflicting beliefs.

Some definitely go along with the Jewish teaching, believing that God's Law was in effect before Moses wrote it down, with only the ceremonial and civil laws being created specifically for Israel following the Exodus as part of the "old" Covenant.

Here are a few examples:

Were the Ten Commandments in Force Before Moses? gives examples of each of the Ten Commandments being obeyed before Moses recorded them.

Did Abraham Keep the Same Commandments God Gave to Moses? | United Church of God

10 Commandments Moses - Life, Hope &amp; Truth