Abu Abd al-Rahman (al-Sulami) said that Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) used to teach us to pray four rak'ahs after the Friday prayer, until we heard the statement of Sayyiduna Ali (may Allah be pleased with him): "Pray six." Abu Abd al-Rahman said: "So we pray six." Ata' said: "Abu Abd al-Rahman used to pray two rak'ahs, then four."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9516