Dawson treats Casey when he risks his life fighting an apartment building fire on Chicago Fire. "Rear View Mirror" is the sixth episode of the show's first season.
Added:

Chicago Fire Season 1 Episode 6 Quotes

Casey: Are you drunk, Chief?
Boden: Yeah...a little.
Casey: I'll be joining you momentarily!
Boden: Good! Glad to hear it.

Enjoy it while you can, this is entrapment.

Voight