Sunnah.com reference : Book 2, Hadith 5Arabic/English book reference : Book 2, Hadith 155
Narrated Jabir (RA), in the version of al-BUkhari and Muslim:
[The Prophet (ﷺ)] used to advance the 'Isha' prayer sometimes and delay it at other times. Whenever he saw the people assembled (for the 'Isha' prayer) he would pray early and if the people delayed, he would delay the prayer. And the Prophet (ﷺ) used to offer the Fajr prayer when it was still dark.
وَعِنْدَهُمَا مِنْ حَدِيثِ جَابِرٍ: { وَالْعِشَاءَ أَحْيَانًا وَأَحْيَانًا: إِذَا رَآهُمْ اِجْتَمَعُوا عَجَّلَ, وَإِذَا رَآهُمْ أَبْطَئُوا أَخَّرَ,  وَالصُّبْحَ: كَانَ اَلنَّبِيَّ ‏- صلى الله عليه وسلم ‏-يُصَلِّيهَا بِغَلَسٍ }   1‏ .‏‏1 ‏- صحيح.‏ رواه البخاري (560)‏، ومسلم (646)‏، واللفظ للبخاري ولفظ مسلم: "والعشاء أحيانا يؤخرها، وأحيانا يعجل".‏