Hadith.1224 - Muhammad ibn Muslim narrated from Imam Muhammad ibn Ali Al-Baqir (as) who said
"The Jumu’ah prayer (Salat al-Jumu'ah) is obligatory upon seven believers: the Imam, his judge, one who claims a right, two witnesses, and the one who executes punishments in front of the Imam. It is not obligatory for fewer than these."