Musnad Ahmad 27:1273

Surayj narrated to us, Abd al-Rahman ibn Zayd ibn Aslam narrated to us, from Zayd ibn Aslam, from Ibn Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Two types of dead animals have been made lawful for us, and two types of blood. As for the two types of dead animals, they are fish and locusts. And as for the two types of blood, they are the liver and the spleen."