Musnad Ahmad 33:852

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Sa‘d ibn Ibrahim, from Muhammad ibn ‘Amr ibn al-Hasan ibn ‘Ali, who said: Al-Hajjaj came to Medina, so we asked Jabir ibn ‘Abd Allah, and he said: "The Messenger of Allah (peace and blessings of Allah be upon him) used to pray Dhuhr when the sun had passed the meridian (al-hajirah), and ‘Asr while the sun was still pure (bright/clear), and Maghrib when it had set, and ‘Isha’—sometimes he would delay it, and sometimes he would hasten it. If he saw that they had gathered, he would hasten, and if he saw that they were slow, he would delay. And as for Subh—he said: They used to, or he said: He used to—pray it in the darkness of the end of the night (ghalas)."