What were Gandalfs final cautionary words as he bade farewell to the dwarves and Bilbo?

Gandalf's final cautionary words to the dwarves and Bilbo before he leaves them to go to Dol Guldur are:

"Be careful!"

He then adds, "And I shall be back in due time."

It's a simple warning, but it emphasizes the dangers they face on their journey and hints at the return of a more powerful Gandalf, ready to confront the growing darkness.