Who said "We have to be careful."?

This quote is attributed to Bucky Barnes (Civil War).

We have to be careful. - Bucky Barnes (Civil War)

"We have to be careful."

Bucky Barnes (Civil War)

"I'm with you till the end of the line."

"That's all that's left, isn't it?"

"You know me."

"I don't know if I'm worth all this."