Genesis 15:1-2, 8

After these things the word of the LORD came to Abram in a vision, saying, “Do not be afraid, Abram. I am your shield, your exceedingly great reward.” But Abram said, “Lord GOD, what will You give me, seeing I go childless, and the heir of my house is Eliezer of Damascus?”

And he said, “Lord GOD, how shall I know that I will inherit it?”