Mughirah narrates from Ibrahim regarding a man who prays alone behind the row that he (Ibrahim) said: "His prayer is complete, but he does not get the multiplied reward."
Note: The Shaykh says that the Prophet (peace and blessings be upon him) negated the extra reward of the congregation, and ordered him to repeat it so that he could obtain the extra reward.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5214