It is transmitted through another chain from a man of Banu Asad that he asked Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him): I pray in my house, then I come to the mosque and find the imam leading the prayer; should I pray with him? Sayyiduna Abu Ayyub (may Allah be pleased with him) said: Yes, pray with him. Whoever does that has a double reward, or he said: a reward equal to that of the whole congregation.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3642