Musnad Ahmad 482:125

Abu Abd al-Rahman narrated to us, Sa’id—meaning Ibn Abi Ayyub—narrated to us, Yazid ibn Abi Habib narrated to me, he said: I heard Abu al-Khayr saying: I saw Abu Tamim al-Jayshani, Abdullah ibn Malik, performing two rak'ahs when he heard the Maghrib adhan. He said: So I came to Uqbah ibn Amir al-Juhani and said to him: "Do you not find it strange, what Abu Tamim al-Jayshani does? He performs two rak'ahs before the Maghrib prayer," and I intended to criticize him for it. Uqbah said: "As for us, we used to do it during the time of the Messenger of Allah, may Allah bless him and grant him peace." I said: "What prevents you from doing it now?" He said: "Being occupied."