A variation of the OP's line is actually found twice in the trilogy Star Trek: Destiny. The first time comes in Book 1, Gods of Night (Chapter 15). The Klingon High Council is debating whether or not to join Starfleet in their war against the Borg. (emphasis mine)
With a clenched jaw and bitter grimace, Kopek extended his open right hand to Martok, who took it. “Qapla’, Chancellor.” A feral gleam shone in his eyes as he released Martok’s hand, turned, and declared with a raised fist, “To war!”
The councillors roared their approval, and Martok flashed a broad, jagged grin. "It is a good day to die … for the Borg."
Later on in Book 2, Mere Mortals (Chapter 4), Captain Krogan of the I.K.S. veScharg'a thinks to himself: It is a good day to die...for my enemies, as he is defending his Klingon homeworld from the Borg. (emphasis mine)
More blasts shook the veScharg’a. Krogan reveled as he watched the viewer and saw the aft-angle view of the torpedoes hitting home and blasting one Borg cube to pieces in a sapphire flash. As the blue fire cloud dissipated into the vacuum of space, another cerulean blast filled the starscape behind it, as the second Borg cube was annihilated.
The bridge officers cheered and roared at their victory. Krogan permitted himself a satisfied growl and a nod of his head. It is a good day to die … for my enemies.