Praise be to Allah.
It is a well established fact in Islam (such that no Muslim has any excuse for not knowing), and the shar’i evidence indicates, that Allaah has not prescribed any prayer at noon time on Fridays except one obligatory prayer for men who are residents and are settled (i.e., not traveling), free and accountable, which is Jumu’ah prayer. If the Muslims do that, then there is no other obligation upon them, be it Zuhr or any other prayer. Jumu’ah prayer is the obligation of that time. The Prophet (peace and blessings of Allaah be upon him), his companions (may Allaah be pleased with them), and the righteous salaf who came after them, did not pray any other obligatory prayer after Jumu’ah. The action to which you refer was introduced many centuries later, and undoubtedly it is one of the newly-invented innovations of which the Prophet (peace and blessings of Allaah be upon him) said: “Beware of newly-invented matters, for every newly-invented matter is an innovation, and every innovation is a going astray.” (Narrated by Abu Dawood, 3991)
And he (peace and blessings of Allaah be upon him) said: “Whoever innovates something in this matter of ours [Islam] that is not part of it will have it rejected.” (Narrated by al-Bukhaari and Muslim). Undoubtedly praying Zuhr after Jumu’ah is something innovated which is not a part of the matter of the Prophet (peace and blessings of Allaah be upon him), so it is to be rejected and is to be included in the innovations and misguidance against which the Prophet (peace and blessings of Allaah be upon him) warned us. The scholars have drawn attention to that, including Shaykh Jamaal al-Deen al-Qaasimi, in his book Islaah al-Masaajid min al-Bida’ wa’l-‘Awaa’id and Shaykh Muhammad Ahmad ‘Abd al-Salaam in his book al-Sunan wa’l-Mubtada’aat.
If someone were to say, “We only do that in order to be on the safe side, lest our Jumu’ah prayer was not valid,” our answer is that he should be told that the basic principle is that the Jumu’ah prayer is valid and is sound and that it is not obligatory to pray Zuhr, indeed it is not permissible to do so at the time of Jumu’ah for those for whom Jumu’ah is obligatory. Being on the safe side is prescribed in cases where the way of the Sunnah is not clear, and there is some doubt and uncertainty. But in a case such as this it is not the matter of doubt; rather we know from the evidence that what is obligatory is Jumu’ah prayer only, so it is not permissible to do something else instead or in addition to it on the grounds that this is an action with the intention of being on the safe side, or to institute a new way which Allaah has not prescribed. Praying Zuhr at this time is contrary to the shar’i evidence which is well established and no Muslim has any excuse for not knowing, so we must not do this and we must beware of it. There are no grounds for doing this, rather it comes from the waswaas (insinuating whispers) of the Shaytaan which he whispers to people so as to prevent them from following true guidance and institutes for them a religion which Allaah has not allowed. This is similar to the way in which he makes the idea of “being on the safe side” when doing wudoo’ attractive to them, until he makes wudoo’ a torment for them, and it takes all their time; whenever they have almost finished, he whispers to them that they have not done it properly or they have not done such and such. He does the same thing to some of them in the prayer; when a person says takbeer for the prayer, he whispers to him that he did not say the takbeer, and he keeps whispering to him that he did not say takbeer, and the person keeps on saying takbeer after takbeer, until the first rak’ah is over, or until the recitation or most of it is over. This is one of the traps and snares of the Shaytaan, who is keen to annul the good deeds of the Muslim and make him confused about his religion. We ask Allaah to keep us and all the Muslims safe and sound from his traps, snares and insinuating whispers, for He is the All-Hearing, Ever-Near.
Praying Zuhr after Jumu’ah is a bid’ah and a going astray, instituting a new way which Allaah has not prescribed. We must not do this; we must beware of it and warn people against it, and limit ourselves to doing Jumu’ah prayer only, as was the way of the Messenger of Allaah (peace and blessings of Allaah be upon him), his companions after him and those who have followed them in truth until the present day. This is the truth concerning which there is no doubt. Imaam Maalik ibn Anas (may Allaah have mercy on him) said: “The later generations of this ummah will not be reformed by anything except that by which the first generation was reformed.” This was also the view of other imaams after him. And Allaah is the source of strength.