Jabir bin Abdullah Ansari (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) that Mu'adh (may Allah be pleased with him) would perform the Isha prayer with the Messenger of Allah (peace and blessings be upon him), then go and lead his people in the Isha prayer, which would be a voluntary prayer for him and an obligatory one for the people.
Hadith Referenceالسنن المأثورة / باب ما جاء في الصلاة في السفر / 9
Hadith Takhrijسنن دار قطني: 1/274,275، السنن الكبرى للبيهقي: 3/86.