It is narrated from Ya'qub bin Afif bin al-Musayyib (may Allah have mercy on him) that he asked Sayyiduna Abu Ayyub (may Allah be pleased with him), the Companion of the Messenger of Allah (peace and blessings be upon him), about a man who prays in his house, then comes to the mosque and finds that same prayer (being held in congregation): should he repeat it with the people or not? Sayyiduna Abu Ayyub (may Allah be pleased with him) said: We asked the Messenger of Allah (peace and blessings be upon him) about that, and he (peace and blessings be upon him) said: "Yes, he should repeat it, and it will include him in the share of reward of the congregation (those who take part in it)."
Imam al-Tabarani (may Allah have mercy on him) said: "This hadith is narrated from Sayyiduna Abu Ayyub (may Allah be pleased with him) only with this chain; Bukayr bin al-Ashajj (may Allah have mercy on him) is alone in narrating it."
Hadith Referenceالمعجم الأوسط / باب الميم / 8683
Hadith Takhrij«أخرجه مالك فى «الموطأ» برقم: 438، وأبو داود فى «سننه» برقم: 578، والبيهقي فى «السنن الكبرى» برقم: 3700، 3701، والطبراني فى «الكبير» برقم: 3997، 3998»