What sin did Abraham commit?

Abraham probably committed many sins because Abraham was a man, and to sin is the nature of mankind. For example, twice he lied about his wife, said she was his sister.

Jewish answer:

Abraham committed zero sins. The Torah records not a single sin on his part. Rather, God himself says (Genesis ch.26): "Abraham hearkened to My voice, and kept My charge, My commandments, My statutes, and My laws."

When Abraham said that Sarah was his sister, he himself later explained (Genesis ch.12 and ch.20) that it was because he feared for his life. Neither Pharaoh nor Abimelech argued with this explanation.