And Abimelech said to Abraham, “What have you encountered, that you have done this thing?” Abraham said, “Because I thought, surely there is no fear of God in this place, and they will kill me because of my wife.
Genesis 20:10-11 (NASB)
In Hebrew, Abimelech actually asks "מָ֣ה רָאִ֔יתָ," which means "What did you see?"
Abraham's response is often written as "I thought," but it is אָמַ֗רְתִּי, which actually means "I said," which means he told his people.
Notice that Abraham never actually answers Abimelech's question. Perhaps he didn't actually see anything. He was simply afraid.