´It was narrated that Ubayy bin Ka'b said:` "The Messenger of Allah said: 'The prayer of a man in congregation is higher than his prayer on his own by twenty-four or twenty-five levels."
Hadith Referenceسنن ابن ماجه / كتاب المساجد والجماعات / 790
Hadith Gradingالألبانی:صحيح دون قوله أربعا وعشرين | زبیر علی زئی:حسن