这里，我将参考“牢不可破的誓言”和“冰霜圣诞节”中的内容来证明斯内普对邓不利多的忠诚。

Here I will reference some quotes from the chapter "the Unbreakable Vow" and "a Very Frosty Christmas" to examine them from the point of view that Snape is loyal to Dumbledore.

youdao

如果你会在那儿保护他……西弗勒斯，你肯发誓么？你能立下牢不可破的誓言么？

If you are there to protect him... severus will you swear it? Will you make the unbreakable vow?

youdao

“是，斯内普说要帮他！”哈利说，“他说答应过马尔福的妈妈要保护他，而且他还立过一个牢不可破的誓言什么的——”。

"Yes, Snape was offering to help him!" said Harry. "he said he'd promised Malfoy's mother to protect him, that he'd made an Unbreakable Oath or something -".

youdao