(21) باب وَقْتِ الْعِشَاءِ إِذَا اجْتَمَعَ النَّاسُ أَوْ تَأَخَّرُوا
Narrated Muhammad bin `Amr:
We asked Jabir bin `Abdullah about the prayers of the Prophet (ﷺ) . He said, "He used to pray Zuhr prayer at midday, the `Asr when the sun was still hot, and the Maghrib after sunset (at its stated time). The `Isha was offered early if the people gathered, and used to be delayed if their number was less; and the morning prayer was offered when it was still dark. "
Reference: Sahih al-Bukhari 565
In-book reference: Book 9, Hadith 42
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 10, Hadith 540