'Tom how could you be so noble'- Who said this statement and why ?

Becky says this to Tom for taking the blame for the torn book and also taking what would have been her whipping.

Rebecca Thatcher” [Tom glanced at her face—it was white with terror]—“did you tear—no, look me in the face” [her hands rose in appeal]—“did you tear this book?”

A thought shot like lightning through Tom’s brain. He sprang to his feet and shouted—“I done it!”

The school stared in perplexity at this incredible folly. Tom stood a moment, to gather his dismembered faculties; and when he stepped forward to go to his punishment the surprise, the gratitude, the adoration that shone upon him out of poor Becky’s eyes seemed pay enough for a hundred floggings. Inspired by the splendor of his own act, he took without an outcry the most merciless flaying that even Mr. Dobbins had ever administered; and also received with indifference the added cruelty of a command to remain two hours after school should be dismissed—for he knew who would wait for him outside till his captivity was done, and not count the tedious time as loss, either.

Tom went to bed that night planning vengeance against Alfred Temple; for with shame and repentance Becky had told him all, not forgetting her own treachery; but even the longing for vengeance had to give way, soon, to pleasanter musings, and he fell asleep at last with Becky’s latest words lingering dreamily in his ear—

“Tom, how could you be so noble!”