Ata' (may Allah have mercy on him) narrates from Jabir (may Allah be pleased with him) that the Sunnah is: "For every three there should be an imam, and when the people are forty or more, the Friday prayer, Eid al-Fitr and Eid al-Adha are obligatory, because they are a congregation."
Only Abd al-Aziz al-Qurashi narrated it, and he is da'if (weak); reliance is upon what has preceded and what is to come, if Allah Almighty wills.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5607