Zechariah asked the angel, “How can I know that this will happen? I’m an old man, and my wife is old too.”
“How will this be,” Mary asked the angel, “since I’m a virgin?”
But they didn’t have children, because Elizabeth was infertile, and by that point they were both very old.
Abraham’s faith didn’t become any weaker even when he thought about the fact that he was now too old have children (he was about 100 years old) and that Sarah had never been able to have children.