Saphira

Eragon, you must amend the spell you are using to warm yourself to include Saphira and me. It is going to grow cold, colder than even the bitterest winter in the Spine, and without magic, we shall freeze to death.

Even you?

I will crack like a piece of hot glass dropped in snow. Next you must cast a spell to gather the air around you and Saphira and to hold it there, so you may still breathe. But it must also allow the stale air to escape, or else you will suffocate. The wording of the spell is complicated, and you must not make any mistakes, so listen carefully. It goes as such—

Once Glaedr had recited the necessary phrases in the ancient language, Eragon repeated them back to him, and when the dragon was satisfied with his pronunciation, Eragon cast the spell. Then he amended his other piece of magic as Glaedr had instructed, so the three of them were shielded from the cold.

Inheritance: A crown of Ice and Snow