Musannaf Ibn Abi Shayba 3:982

Waki’ narrated to us, he said: Shu’bah narrated to us, from Abu Bishr, from Sa’id ibn Jubayr; and Shu’bah [also narrated] from Najiyah ibn Hassan, from Ibn Abi Layla, from Umar, who said: "That I witness the Isha and the Fajr [prayers] in congregation is more beloved to me than that I spend the time between them in prayer."