Answer:
It's physically impossible. You'd have to go to the nether and kill one of the nether slimes.
Explanation:
Or you can just cheat, give yourself creative and give yourself a fire res potion. Plus, you can't brew anything without a brewing stand or nether wart.
Answer:
Get a trident from a drowned and enchant it with Channeling and strike a villager with it. Contain the witch and burn it using flint&steel. It will try to drink the potion, but kill it as fast as you can. There now you can go through the Nether portal without having to worry about lava.
Explanation:
