Musnad Abu Ya'la al-Mawsili 109:30

Ishaq ibn Abi Isra'il narrated to us, Nadr narrated to us, Shu'bah narrated to us, from Sa'd, who said: I heard Muhammad ibn 'Amr say: Al-Hajjaj arrived and he used to delay the prayer. We asked Jabir ibn 'Abd Allah about that, and he said: The Messenger of Allah (ﷺ) used to pray Dhuhr in the midday heat when the sun passed its zenith, and 'Asr while the sun was still pure (bright), and Maghrib when the sun set. As for 'Isha', he would sometimes delay it and sometimes hasten it. If he saw that the people had gathered, he would hasten it, and if he saw that they were late, he would delay it. And he used to pray Subh (Fajr) in the darkness before dawn.