"She [Trelawney] says the crystal ball's told her that, if I tell you, I'll have a horrible accident!" squeaked Neville…

OotP:

"My gran says that's rubbish," piped up Neville. "She says it's the Daily Prophet that's going downhill, not Dumbledore. She's cancelled our subscription. We believe Harry," he said simply. He climbed into bed and pulled the covers up to his chin, looking owlishly over them at Seamus. "My gran's always said You-Know-Who would come back one day. She says if Dumbledore says he's back, he's back."
~~~
"And in our first year," said Neville to the group at large, "he saved that Philological Stone –"
"Philosopher's," hissed Hermione.
"Yes, that – from You-Know-Who," finished Neville.
~~~
"Expelliarmus!" said Neville, and Harry, caught unawares, felt his wand fly out of his hand.
"I DID IT!" said Neville gleefully. "I've never done it before – I DID IT!"
~~~
"Harry was pleased to see that all of them, even Zacharias Smith, had been spurred to work harder than ever by the news that ten more Death Eaters were now on the loose, but in nobody was this improvement more pronounced than in Neville. The news of his parents' attacker's escape had wrought a strange and even slightly alarming change in him."

"Just in case they're - busy - and you get the chance - "
"Kill the snake?"
"Kill the snake," Harry repeated.
"All right, Harry. You're okay, are you?"
"I'm fine. Thanks, Neville."
But Neville seized his wrist as Harry made to move on.
"We're all going to keep fighting, Harry. You know that?"
~~~
"But you are a pure-blood, aren't you, my brave boy?" Voldemort asked Neville, who stood facing him, his empty hands curled into fists.
"So what if I am?" said Neville loudly.
"You show spirit, and bravery, and you come of noble stock. You will make a very valuable Death Eater. We need your kind, Neville Longbottom."
"I'll join you when hell freezes over," said Neville. "Dumbledore's Army!" he shouted, and there was an answering cheer from the crowd, whom Voldemort's silencing charms seemed unable to hold.