Ahsanul Fataawaa states:

"Q: Salaah-610: Is it permissible to study books of Deen or write Masaa'il or Ahadeeth if one reaches the Masjid before the Adhaan of the Khutbah?

Answer: After the first Adhaan of Jumu'ah it is not permissible to do anything apart from preparing for the Jumu'ah salaah, even though it be an act of Deen.

The gist of it all is that one should finish off with one's bath and all other preparations as soon as possible and then proceed to the Masjid. If one is engaged in one's business or profession in the morning, one should terminate ali such activities early enough to take a bath, change clothing, apply perfume and arrive at the Jaami Masjid in time for the first Adhaan. If it occurred that one was delayed for some good reason and could not take a bath sooner, it will be permissible to do so after the Adhaan on condition that one does not miss the Sunnah Rakaahs before the Jumu'ah salaah and the Khutbah. If there is fear of missing any of the two, one should then only perform wudhu.

The day of Jumu'ah is an extremely auspicious day and the Ahadeeth emphasise proceeding early for the Jumu'ah salaah. The earlier one arrives at the Masjid, the more one is rewarded. A Hadith narrated by Hadhrat Abu Hurayrah RADI. states that the angels stand by the doors of the Masaajid on the day of Jumu'ah to write the names of the people as they arrive one after another. The one to arrive earliest receives the reward of donating a camel in the path of Allaah. The one arriving after him receives the reward of donating a cow in the path of Allaah; the one thereafter, the reward of donating a sheep in the path of Allaah; the one thereafter, the reward of donating a hen in the path of Allaah: the one thereafter, the reward of donating an egg in the path of Allaah. Then when the Imaam stands up to deliver the Khutbah, the angels roll up their scrolls and listen to the remembrance of Allaah.

Another Hadith states that when a person takes a bath on a Friday, makes others (his wife) take a bath, leaves early for the salaah on foot, sits close to the Imaam, listens attentively to the Khutbah and does nothing futile, he will receive the reward of a year's Ibaadah and a year's fasting for every step that he takes.

One should therefore proceed as early as possible, as was the practice of the Sahabah RADI.; and all the pious predecessors. Behisti Gohar quotes from Imaam Ghazaali RADI. that during previous times, the streets were seen full of people after the Fajr salaah as they proceeded to the Jaami Masjid for the Jumu'ah salaah. The crowds were as much as those of Eid. It was when this ceased that people complained of it being the first new practice in Islaam. After stating this, Imaam Ghazaali RAH. laments that this is indeed a shameful state of affairs when it is seen that the Jews and Christians proceed early on Saturdays and Sundays to their synagogues and churches and the seekers of worldly wealth proceed early to the marketplaces. Why then, he says, do the seekers of the Aakhirah not put their best step forward?
It is sad to note that Muslims today do not value this great day of Jumu'ah which the early Muslim revered more greatly than the days of Eid, that was a token of honour for Rasulullaah SAW. and which the previous Ummahs were deprived of. The Muslims have wasted this great bounty and the ill effects of it are apparent before us.
Behisti Gohar goes on to state that every Muslim ought to prepare for the day of Jumu'ah from Thursday. They should engage in Istighfaar from after Asr on Thursday, keep their clothing ready for Friday and even made means on Thursday for perfume to be available if not already available. Saints have stated that the person to benefit most from the Jumu'ah is the one who most looks forward to it and starts preparing for it from Thursday. On the other hand, the most unfortunate person is he who does not even know which day it is and has to ask others. In fact, some pious predecessors even spent the night in the Jaami Masjid awaiting the Jumu'ah salaah.
And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2