(a) Al-Zuhri (may Allah have mercy on him) narrates from Umm Abdullah al-Dawsiyyah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "The Friday prayer is obligatory upon every village in which there is an imam, even if they are only four," until the Prophet (peace and blessings be upon him) mentioned three.
(b) Al-Zuhri (may Allah have mercy on him) narrates about Sayyiduna Mus'ab bin Umayr (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) sent him to Madinah, he led them in the Friday prayer while they were twelve men.
Al-Hakam bin Abdullah is matruk (abandoned), Mu'awiyah bin Yahya is da'if (weak), and this is not authentic from al-Zuhri. A hadith about fifty has also been narrated on this subject, but its chain is not authentic.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5617