Exodus 3:13-15, from the NRSV version of the Bible.
But Moses said to God, “If I come to the Israelites and say to them, ‘The God of your ancestors has sent me to you,’ and they ask me, ‘What is his name?’ what shall I say to them?”
God said to Moses, “I AM WHO I AM.” He said further, “Thus you shall say to the Israelites, ‘I AM has sent me to you.’”
God also said to Moses, “Thus you shall say to the Israelites, ‘The LORD, the God of your ancestors, the God of Abraham, the God of Isaac, and the God of Jacob, has sent me to you’: This is my name forever, and this my title for all generations.