Musnad Ahmad 788:82

'Ali ibn 'Abdullah narrated to us, Husayn ibn 'Ali al-Ju'fi narrated to us, from Mujammi' ibn Yahya ibn Zayd ibn Jariyah al-Ansari, who said: I heard him mentioning it, from Sa'id ibn Abi Burdah, from Abi Burdah, from Abu Musa, who said: We prayed the Maghrib prayer with the Messenger of Allah, may Allah bless him and grant him peace. Then we said: "If only we waited until we prayed the 'Isha prayer with him." He said: So we waited, and he came out to us and said: "Are you still here?" We said: "Yes, O Messenger of Allah. We said: We will pray the 'Isha prayer with you." He said: "You have done well," or "You have done right." Then he raised his head toward the sky—and he used to raise his head toward the sky often—and he said: "The stars are a security for the sky; so when the stars depart, what is promised to the sky will come to it. And I am a security for my companions; so when I depart, what is promised to my companions will come to them. And my companions are a security for my nation; so when my companions depart, what is promised to my nation will come to them."