Midrasz do Diwrej ha-jamim II 33:1

R. Akiva: "It is written (II Chronicles 33:1) 'Menasheh was twelve years old when he began to reign, and he reigned fifty-five years in Jerusalem.' And it is written (Proverbs 25:1) 'These, too, are the proverbs of Solomon, which were copied down by the servants of Chezkiah king of Judah.' Now would it enter your mind that Chizkiyahu taught Torah to all of Israel but not to Menasheh his son? But (it is to be understood that) of all the Torah he taught him and all the toil he invested in him naught availed him but afflictions, as it is written (II Chronicles 33:10-13) 'And the L-rd spoke to Menasheh and his people, but they did not listen. And the L-rd brought against them the officers of the king of Ashur's army. And they caught Menasheh with hunting hooks, and bound him in chains and led him to Bavel. And in his suffering he besought the L-rd his G-d, and he humbled himself greatly before the G-d of his fathers. And he prayed to Him, and He was entreated of Him, and He heard his supplication, and He returned him to Jerusalem to his kingdom" — whence we derive that afflictions are beloved.