Série de livros
Parece que o primeiro casting de Harry de um patronus foi na frente de toda a escola durante o jogo de Quadribol:
Distracted, Harry looked down.
Three Dementors, three tall, black, hooded Dementors, were looking up at him. He didn’t stop to think. Plunging a hand down the neck of his robes, he whipped out his wand and roared, ‘Expecto patronum!’
Something silver white, something enormous, erupted from the end of his wand. He knew it had shot directly at the Dementors but didn’t pause to watch; his mind still miraculously clear, he looked ahead – he was nearly there. He stretched out the hand still grasping his wand and just managed to close his fingers over the small, struggling Snitch.Harry Potter and the Prison of Azkaban: Chapter 13 - Gryffindor versus Ravenclaw
Dito isso, Oliver Wood observa, enigmaticamente, que Harry tem uma arma secreta contra os dementadores. Como Oriol aponta em seu comentário , eles só falavam em termos de" afastar "os dementadores ao invés de especificamente que ele estaria tentando um Patrono, mas que, então, mendiga a questão de que outras formas existem para afastar um Dementador, se não o Patrono:
‘I can’t see what’s going to stop us tomorrow!’ said Wood. ‘Not unless – Harry, you’ve sorted your Dementor problem, haven’t you?’
‘Yeah,’ said Harry, thinking of his feeble Patronus and wishing it was stronger.Harry Potter and the Prison of Azkaban: Chapter 13 - Gryffindor versus Ravenclaw
Série de filmes
Dentro dos filmes, a ordem dos eventos é diferente. Harry é derrubado de sua vassoura na partida de Quadribol (nunca escalando o Patrono) e só o faz na frente de Hermione no final do filme.
