Friday is the day which Allah has made special for this Ummah, the nation of Prophet Muhammad (peace and blessings be upon him), and which Allah has favored above all the other days of the week. It is reported that the Messenger of Allah (peace and blessings be upon him), said: “The best day on which the sun rises is Friday. On this day Adam was created, on this day he entered Paradise and on this day he was expelled from it.” (Muslim)
Sheikh M. S. Al-Munajjid, a prominent Saudi Muslim lecturer and author, states: You can only meet Jumu`ah Prayer if you meet one rak`ah with the imam, and that means meeting the ruku` (bowing) with the imam. If you catch up with the imam before he stands up from the ruku` in the second rak`ah, then you have caught the Prayer, and you should then complete your Prayer after the imam says the salam by standing up and completing the remaining rak`ah of your Prayer. But if you join the imam after he has stood up from the ruku` of the second rak`ah, this means that you have missed Jumu`ah Prayer and have not caught it.
In this case you have to pray Zhuhr, so you should stand up after the imam has said the salam and complete your Prayer with four rak`ahs because it is Zhuhr and not Jumu`ah. This is the view of the majority of scholars, Malik, Ash-Shafi`i and Ahmad (may Allah have mercy on them). They quoted several texts as evidence, such as:
1. The words of the Prophet (peace and blessings be upon him): “Whoever catches up with one rak`ah of the Prayer has caught up with the Prayer” (Al-Bukhari and Muslim).
2. The report narrated by An-Nasa’i from `Abdullah ibn `Umar (may Allah be pleased with them both), who said: “The Messenger of Allah (peace and blessings be upon him) said: ‘Whoever catches up with one rak`ah of Jumu`ah or any other Prayer, let him add more rak`ahs to it to complete his Prayer.’”
If a person does not catch the Prayer for a reason that is beyond his control—such as the bus breaking down or other excuses such as falling asleep or forgetting—then there is no sin on him in that case because Allah says: “And there is no sin on you concerning that in which you made a mistake, except in regard to what your hearts deliberately intend” (Al-Ahzab: 5).
A person in this case does not deliberately intend to miss the Prayer.
And the Prophet (peace and blessings be upon him) said, “Allah has forgiven my Ummah for what they forget and what they do by mistake, and for what they are forced to do” (Ibn Majah).
Although, according to Abu Hanifah, if one catches the Tashahhud with the imam, then he has caught the Jumu`ah.