Genesis 22: 6-7 says, 6 And Abraham took the wood of the burnt offering, and laid it upon Isaac his son; and he took the fire in his hand, and a knife; and they went both of them together. 7 And Isaac spake unto Abraham his father, and said, My father: and he said, Here am I, my son. And he said, Behold the fire and the wood: but where is the lamb for a burnt offering?
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
We just don't know how Abraham carried "the fire." Maybe he carried a live coal or a flint to start a fire. LASB
Sometimes it helps if you look up the verse in many different translations. Here are 4 good suggestions:
CEV
Isaac said, “Father, we have the coals and the wood, but where is the lamb for the sacrifice?” “My son,” Abraham answered, “God will provide the lamb.” The two of them walked on, and...
EXB
Isaac said to his father Abraham, “Father!” Abraham answered, “Yes, my son.” Isaac said, “We have the ·fire [or tinder] and the wood, but where is the ·lamb [sheep] ·we will burn as a sacrifice [L for the whole burnt offering]?”
GW
Isaac spoke up and said, “Father?” “Yes, Son?” Abraham answered. Isaac asked, “We have the burning coals and the wood, but where is the lamb for the burnt offering?”
GNT
Isaac spoke up, “Father!” He answered, “Yes, my son?” Isaac asked, “I see that you have the coals and the wood, but where is the lamb for the sacrifice?"