Musnad Ahmad 25:431

Yunus narrated to us, Hammad—meaning Ibn Zayd—narrated to us, from Al-Zubayr—meaning Ibn Khurayt—from Abdullah ibn Shaqiq, who said: Ibn Abbas delivered a sermon to us one day after the afternoon prayer (Asr), until the sun set and the stars appeared. The people began calling out to him: "The prayer, the prayer!" Among the people was a man from Banu Tamim, and he kept saying: "The prayer, the prayer!" He (Ibn Abbas) became angry and said: "Are you teaching me the Sunnah? I witnessed the Messenger of Allah (peace and blessings of Allah be upon him) combine the Dhuhr and Asr prayers, and the Maghrib and Isha prayers." Abdullah said: I felt something in myself regarding that, so I met Abu Hurayrah and asked him, and he agreed with him.