Musannaf Ibn Abi Shayba 3:971

Muhammad bin Bishr narrated to us, he said: Muhammad bin ‘Amr narrated to us, he said: ‘Abd al-‘Aziz bin ‘Amr bin Damrah narrated to us, from a man from Juhaynah, who said: I asked the Messenger of Allah, may Allah bless him and grant him peace, "When should I pray the Isha?" He said: "When the night fills the belly of every valley."