Musnad Ahmad 27:711

Yahya narrated to us, from Ubaydullah, Nafi’ informed me, from Ibn Umar, from the Prophet (peace and blessings of Allah be upon him), who said: "There is no blame upon the one who kills five of the animals while he is in the state of ihram: the scorpion, the mouse, the crow, the kite, and the vicious dog."