What is the Torah?
The answer depends on the context.
Torah can simply mean instruction. Or it can refer to the five books of Moses. Or it can refer to the 613 commandments derived from the five books of Moses.
When rabbis speak of the Torah, they often mean the 613 commandments of Moses. And when they are asked if Abraham obeyed the Torah, they answer “Yes”. But they do not distinguish between the Law of Moses and the Torah that Abraham followed. This is troubling, because we know they were different, if not by a lot, then by a little.
How do we know this?
Abraham did not tithe to the Levites, as required by Moses
Abraham did not observe the Passover, as required by Moses.
Abraham did not observe Yom Kippur, as required by Moses.
Since Abraham predated both the tribe of Levi and the exodus from Egypt, he could not follow commands that had no meaning in his day.
Listen below to Rabbi Tovia Singer explaining how Abraham obeyed the Torah. This is an example of how Orthodox teaching adds to Tanakh, for Tanakh knows nothing of Abraham obeying the Law of Moses.