Dawud bin Abi Hind (may Allah have mercy on him) said: I asked Sa'id bin al-Musayyib (may Allah have mercy on him) about a man who prays in his house and then also finds the congregation. He said: He should pray with the congregation as well. I said: For which of the two prayers will he receive the reward of the obligatory prayer? He said: For the one he prayed in congregation, because Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrated to us that the Messenger of Allah (peace and blessings be upon him) said: "Prayer in congregation is (in reward) twenty-five times greater than the prayer of one praying alone."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3648