When any one of you observes the Jumu'a prayer (two obligatory rak'ahs in congregation), he should observe four (rak'ahs) afterwards. (Using translation from Muslim 881a)
قَالَ رَسُولُ اللهِ ﷺ «إِذَا صَلَّى أَحَدُكُمُ الْجُمُعَةَ فَلْيُصَلِّ بَعْدَهَا أَرْبَعًا»