After you get a raft and escape the Solitary Island, you reach a continent that contains Albrook and Tzen.

Go Toward Tzen

If you have not equipped Celes, be sure to do so. Then you can go to Albrook to the west if you wish. Otherwise, go north to Tzen.

Go north in Tzen. Kefka's Light of Judgement will hit the town. Go farther north, past all the running people, and you will find Sabin. Go into the house that he is holding up.

Equip Sprint Shoes, as well as a Ribbon, or at least a a relic that protects against Poison and Petrify, and preferably Stop.

Pm Stalker/Nightwalker is weak to Fire and Pearl/Holy. It is Undead, so Cure spells will heal it, and Fenix Downs/Phoenix Downs will kill it.

HermitCrab/HrmtCrab/Zokka can cast Stone and Stop. Celes should use level 2 spells such as Fire 2/Fira. If that is not possible, it might be better to just run.

Scorpions have high defense against both magic and regular attacks. They can also cast Doom/Death. Level 2 spells are the best option to defeat them, but it is probably faster to just run away.

Run in and go north. Open the chest north of the table to get a Heal Rod/Healing Rod, then go west. Go south to enter the room, and open the chest there to get a Pearl Rod/Holy Rod. Go south to exit this room, and go all the way west to find another chest. It contains a Hyper Wrist. Go north, but ignore the stairs and chest, and go north to find another chest. It contains a Tincture/Ether. Then go south again. Ignore the chest by the stairs (it contains a Monster-in-a-box), and go down the stairs.

Go north through the door, then go west and south to find a chest. It contains Drainer/Blood Sword. Then go to the northeast corner of the room and open the chest there to get Magicite. Then go west and talk to the boy at the fireplace. Ignore the chest in the top left (it contains another Monster-in-a-box) and just go to the southeast corner of the room, go up the stairs, go north, east, and south at the fireplace to leave the house.

Sabin joins you. Be sure to equip him.

You can buy the Sraphim/Seraph Esper from the bandit in the northeast trees if you didn't before.