Genesis 15:8

But he said, "O Lord GOD, how am I to know that I shall possess it?"

And Zechariah said to the angel, "How shall I know this? For I am an old man, and my wife is advanced in years."

Then Gideon said to God, "If you will save Israel by my hand, as you have said,

And Hezekiah said to Isaiah, "What shall be the sign that the LORD will heal me, and that I shall go up to the house of the LORD on the third day?"

Show me a sign of your favor, that those who hate me may see and be put to shame because you, LORD, have helped me and comforted me.

"Ask a sign of the LORD your God; let it be deep as Sheol or high as heaven."

And Abraham said to his servant, the oldest of his household, who had charge of all that he had, "Put your hand under my thigh,

Behold, I am standing by the spring of water, and the daughters of the men of the city are coming out to draw water.

And he said to him, "If now I have found favor in your eyes, then show me a sign that it is you who speak with me.

If they say to us, 'Wait until we come to you,' then we will stand still in our place, and we will not go up to them.

And Mary said to the angel, "How will this be, since I am a virgin?"

Treasury of Scripture Knowledge