Musnad Ahmad 1060:85

Muhammad ibn Abi ‘Adi narrated to us, from Muhammad ibn Ishaq, who said: Yazid ibn Abi Habib narrated to me, from Marthad ibn ‘Abdullah, who said: Abu Ayyub came to us, and ‘Uqbah ibn ‘Amir was in Egypt at that time, and he delayed the Maghrib prayer. Abu Ayyub stood up to him and said: "What is this prayer, O ‘Uqbah?" He said: "We were occupied." He said: "As for me, by Allah, it is only that I fear people will think that you saw the Messenger of Allah (peace and blessings of Allah be upon him) doing this. Have you not heard the Messenger of Allah (peace and blessings of Allah be upon him) say: 'My nation will continue to be in a state of goodness, or upon the natural disposition (fitrah), as long as they do not delay the Maghrib prayer until the stars become intertwined'?"