Redemption Armor

Redemption Armor is the Tier 3 set for paladins.

Source
The set was unobtainable with the introduction of Wrath of the Lich King, but was later reintroduced and made available in the Black Market Auction House.

Source before Patch 2.4.3
Most Tier 3 items can be acquired through quests given by Eligor Dawnbringer, who can be found in Light's Hope Chapel in the Eastern Plaguelands. Before the quests become active, Echoes of War must be completed.

The quests require several crafting materials, s (which drop from Trash Mobs in Naxxramas) as well as a token from a boss in Naxxramas

The only exception is the, which drops directly from Kel'Thuzad in Naxxramas