Assalamualaikum ustaz. What is the ruling of taking notes when the khatib is delivering the Friday sermon?
Waalaikumussalam wrt. wbt.,
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions, and all those who follow his footsteps until the Final day.
Basically, two general matters make a person considered to be unmindful (lagha) of his Friday prayer. We detailed them as follows:
There is a hadith from the Prophet PBUH which restricts a person from talking when the khatib is delivering the sermon. From Abu Hurairah RA, the Prophet PBUH said:
إِذَا قُلْتَ لِصَاحِبِكَ يَوْمَ الجُمُعَةِ: أَنْصِتْ، وَالإِمَامُ يَخْطُبُ، فَقَدْ لَغَوْتَ
“On Friday, when the Imam is delivering the Khutbah (religious talk), if you say to your companion to keep quiet, then indeed you have committed a sin (error/something senseless).” 
Saidina Ali RA said, “Whoever did something useless then it means he doesn’t attain anything from his Friday prayer.” This means the person loses the advantages of Friday that is commanded and its rewards are hoped. 
Scholars have agreed that it is afdhal (prioritized) for whoever is listening to the sermon of the imam to stay silent and listen attentively. This is prioritized over him reciting dhikr by himself, reciting the Quran or supplicating. 
Any movement and actions will result in a person losing focus and being distracted from the sermon being delivered hence making it a useless act. This is based on a narration from Abu Hurairah RA, where the Prophet PBUH said:
مَنْ تَوَضَّأَ فَأَحْسَنَ الْوُضُوءَ ثُمَّ أَتَى الْجُمُعَةَ فَاسْتَمَعَ وَأَنْصَتَ غُفِرَ لَهُ مَا بَيْنَهُ وَبَيْنَ الْجُمُعَةِ وَزِيَادَةُ ثَلاَثَةِ أَيَّامٍ وَمَنْ مَسَّ الْحَصَى فَقَدْ لَغَا
“If anyone performs ablution, doing it well, then comes to the Friday prayer, listens and keeps silent, his sins between that time and the next Friday will be forgiven him, with three days extra; but he who touches pebbles has caused an interruption (lagha).” 
According to the above hadith, it can be understood that the act of playing with pebbles while the khatib is delivering the sermon is restricted and its doer has caused lagha. This matter is widened to encompass any other actions that result in a person losing focus and getting distracted from listening to the sermon. For example, playing with one’s phone, sleeping, eating, drink without any reason or need.
The issue of taking notes during the Friday sermon
Basically, it is sunnah for a person who is listening to the Friday sermon to keep quiet and not talk or do any other activities other than listening to the khatib.
This is based on a hadith from Salman al-Farisi RA who said: Rasullullah PBUH said:
لاَ يَغْتَسِلُ رَجُلٌ يَوْمَ الْجُمُعَةِ، وَيَتَطَهَّرُ مَا اسْتَطَاعَ مِنْ طُهْرٍ، وَيَدَّهِنُ مِنْ دُهْنِهِ، أَوْ يَمَسُّ مِنْ طِيبِ بَيْتِهِ ثُمَّ يَخْرُجُ، فَلاَ يُفَرِّقُ بَيْنَ اثْنَيْنِ، ثُمَّ يُصَلِّى مَا كُتِبَ لَهُ، ثُمَّ يُنْصِتُ إِذَا تَكَلَّمَ الإِمَامُ، إِلاَّ غُفِرَ لَهُ مَا بَيْنَهُ وَبَيْنَ الْجُمُعَةِ الأُخْرَى
“If any man bathes on Friday, purifies himself as much as he can with ablution, anoints himself with oil, or puts on a touch of perfume which he has in his house, then goes out and, without squeezing between two men, prays what is prescribed for him, then remains silent when the imam speaks, his sins between that time and the next Friday will be forgiven him.” 
From Abu Hurairah RA, the Prophet PBUH said:
إِذَا قُلْتَ لِصَاحِبِكَ يَوْمَ الْجُمُعَةِ أَنْصِتْ. وَالإِمَامُ يَخْطُبُ فَقَدْ لَغَوْتَ
“If you say to your companion to keep quiet, then indeed you have committed a sin (error/something senseless).” 
Saidina Ali narrated:
وَمَنْ لَغَا فَلَيْسَ لَهُ فِى جُمُعَتِهِ تِلْكَ شَىْءٌ
“Anyone who involves in idleness (during the sermon) will receive nothing (no reward) on that Friday.” 
The restriction of talking here includes writing to prevent artifice such as a person using SMS, WhatsApp or others when the khatib is delivering the sermon but claims “I’m not talking, just writing.”
This is strengthened with a hadith from Abu Hurairah RA:
مَنْ مَسَّ الْحَصَى فَقَدْ لَغَا
“Whoever smoothes the pebbles, then he has engaged in Laghw.”* *Meaning he has done what is not suitable. 
Imam al-Nawawi said: “In the hadith, there is a restriction against playing with pebbles and other similar acts, for it is included as idle acts during a sermon (Friday sermon). Here, there is also an indication to focus one’s heart and body solely on the sermon.” 
There is an opinion stating that taking notes during the sermon is not included in the restriction because it is done to increase one’s attention and understanding. This is different from rebuking another congregant to keep quiet or playing with pebbles. However, a response to this opinion stated that writing or taking notes doesn’t necessarily make a person more focused on the contents of the sermon. It is common for a person to miss some contents of the sermon because he is busy writing. Furthermore, the act of him writing the contents of the sermon may lead to fitnah by attracting attention to himself for those who are sitting beside or near him looking at what he is doing for writing during a sermon is not a common practice.
Thus, we are inclined to state that the ruling of taking notes during the Friday sermon is that it is prioritized to leave such an act. It is better if the person gives his full attention, hearing and actions towards the contents of the sermon. Moreover, a person can easily access or get the sermon’s text from the Religious Department or use a voice recorder should he want to have it.
Regarding the conditions of the sermon, where it is obligatory for 40 residents of whom it is obligatory on them to perform the Friday prayer, for the ruling of the sermon, it is still valid because a person writing still listens to the sermon although he is taking notes. May Allah SWT grant us the blessing of strength in performing our worship the best way we can.
 Narrated by al-Bukhari (934)
 Narrated by al-Bukhari (843)
 Narrated by al-Bukhari (892) and Muslim (851)
 Narrated by Abu Daud (1051)
 See al-Minhaj Syarh Sahih Muslim, 3/229