It is narrated from Sayyiduna Abu Waqid al-Laythi (may Allah be pleased with him) that the Companions said: O Messenger of Allah! We live in a land where we are afflicted by the hardship of hunger, so what is lawful for us of carrion? He (peace and blessings be upon him) said: "When you have no evening milk, no morning milk, and not even any greens, then you may eat of it."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3302