If the Imam reads surat al-Insan, and surat s-Sajdah in the Fajr prayer on a Juma’ah day then he has followed the sunnah. If he does not read these two surahs, then his prayer is valid and there is no wrong on him. There is no doubt that the sajdah at the time of fajr is not obligatory.
Dr Hussam al Deen bin Musa Afana- A teacher of jurisprudence and its origins in the University of Al-Quds Palestine- says:
Its is confirmed that the Prophet ﷺ used to read surat s-Sajdahin the Fajr prayer on the day of Juma’ah
1. On the authority of ibn Abbas (RA) (that the Prophet ﷺ used to recite in the fajr salah on a Juma’ah, surat s-Sajdah (Alif Laam Meem, The revelation of the Book, without a doubt…) and surat al-Insan (Has there come upon man a period of time…) – Narrated by Muslim.
2. On the authority of Abu Hurayrah that the Prophet ﷺ used to recite in the morning of Juma’ah: (Alif Laam Meem, The revelation of the Book, without a doubt…) in the first raka’h and in the second rak’ah he would recite (Has there come upon man a period of time when he was nothing to be mentioned) narrated by Muslim.
From these two hadiths we can say that it was preferred and liked to read surat us-Sajdah and surat al-Insan in the Fajr prayer on the day of Juma’ah.
The people of knowledge have interpreted that the reason for reading surat us-Sajdah and surat al-Insan, is not because of the sajdah in the first surah, but rather the deep powerful meanings which the two surahs contain. And for that reason it is disliked to read both surahs repeatedly, in case people begin to think it is compulsory to read these two surahs. Some people have thought that the Imam must read any surah with a sajdah (prostration) in it, in the fajr prayer on the day of Juma’ah, this is wrong thinking because the sajdah (prostration) isn’t what is meant necessarily, and it is actually the surah which is meant, that is, surah Sajdah. Therefore, there is no compulsion for the Imam to read any surah with a sajdah (prostration) in it.
The scholar Ibn Al Qayyim said: The prophet ﷺ used to read in the fajr salah- on a Juma’ah- the two surahs : (Alif Laam Meem, The revelation of the Book, without a doubt…) and surat al-Insan (Has there come upon man a period of time…) and a lot of people who do not have knowledge think that the reason behind reading these two particular surahs is to add an extra sajdah (prostration) and they call it the sajdah of Juma’ah, and if one of them do not read these two particular surahs then people prefer that he read another surah with a sajdah (prostration) in it. For this reason, it is disliked by the scholars to repeatedly read these surahs in the Fajr prayer on a Juma’ah to avoid ignorant people saying such things.
Shiekh Al Islam Ibn taymiyah said: The Prophet ﷺ used to read these two surahs in the fajr salah- on the day of Juma’ah- because they encompass what was in this day, as they both contain the creation of Adam, and they mention the resurrection, and the bringing together of the slaves and that will be on the day of Juma’ah. Reading these surahs on a Juma’ah reminds the Muslim community what will happen on this day, and the sajdah (prostration) came following all of these and not the purpose for why one should read that particular surah, as this is one of the characteristics of the day of Juma’ah) [Zad Al Ma’aad 1/375].
Imam Al-Qarafi said in his text: It became popular for the people of Egypt that the morning prayer on a Juma’ah has three raka’hs rather than two, this is because they see the Imam reads surah sajdah frequently and does sujood, and so they think that this is another compulsory raka’ah. It’s then incumbent to put an end to the means that make the people hold such thought) [Al Furuq 12/191].