It is narrated from Jabir (may Allah be pleased with him) that Mu'adh (may Allah be pleased with him) would perform the 'Isha prayer with the Prophet (peace and blessings of Allah be upon him), then go to his own people and lead them in the same prayer. For Mu'adh (may Allah be pleased with him), this prayer would be voluntary, while for his people it would be the obligatory 'Isha prayer.
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 304
Hadith Takhrijاخرجہ البخاری: الاذان، باب اذا صلی ثم ام قوما: 711، 700، ومسلم، الصلاة، باب القراءۃ فی العشاء: 465۔