وَإِذَا قِيلَ لَهُمُ اتَّبِعُوا مَا أَنْزَلَ اللَّهُ قَالُوا بَلْ نَتَّبِعُ مَا وَجَدْنَا عَلَيْهِ آبَاءَنَا أَوَلَوْ كَانَ الشَّيْطَانُ يَدْعُوهُمْ إِلَى عَذَابِ السَّعِيرِ ﴿۲۱﴾ وَمَنْ يُسْلِمْ وَجْهَهُ إِلَى اللَّهِ وَهُوَ مُحْسِنٌ فَقَدِ اسْتَمْسَكَ بِالْعُرْوَةِ الْوُثْقَى وَإِلَى اللَّهِ عَاقِبَةُ الْأُمُورِ ﴿۲۲﴾ وَمَنْ كَفَرَ فَلَا يَحْزُنْكَ كُفْرُهُ إِلَيْنَا مَرْجِعُهُمْ فَنُنَبِّئُهُمْ بِمَا عَمِلُوا إِنَّ اللَّهَ عَلِيمٌ بِذَاتِ الصُّدُورِ ﴿۲۳﴾

﴾21﴿ Wa izaa qeela lahumut-tabi'oo maaa anzalal laahu qaaloo bal nattabi'u maa wajadnaa 'alaihi aabaaa'anaa; awalaw kaanash Shaitaanu yad'oohum ilaa 'azaabis sa'eer
﴾22﴿ Wa many yuslim wajha hooo ilal laahi wa huwa muhsinun faqadistamsaka bil'ur watil wusqaa; wa ilal laahi 'aaqibatul umoor
﴾23﴿ Wa man kafara falaa yahzunka kufruh; ilainaa marji'uhum fanunabbi'uhum bimaa 'amiloo; innal laaha 'aleemum bizaatis sudoor

﴾21﴿ And when it is said to them, "Follow what Allah has revealed," they say, "Rather, we follow what we found our forefathers upon." Even though their forefathers were inviting them to the blazing fire
﴾22﴿ And whoever submits their face (self) to Allah while being sincere, then they have grasped the firmest handhold. And to Allah alone is the end of all matters
﴾23﴿ And whoever disbelieves, let not their disbelief grieve you. To Us is their return, and We will inform them of what they have done. Indeed, Allah is All-Knowing of what is in the hearts

[21] This is torment—meaning they have no reasoning, but they follow the imitation of their forefathers. And this is mentioned in contrast to "without knowledge", so it is clear that such imitation is not based on knowledge.
By "our forefathers" (آبَاءَنَا), what is meant are the great scholars and elders, not merely biological fathers.
Such verses have also appeared in Surah al-Baqarah (2:170), Surah al-Ma’idah (5:104), and Surah al-Zukhruf (43:22–23).
[22] Since the state of the polytheist and his weak argument was mentioned, now in this verse the state of the monotheist and the strength of his argument is described.
“And whoever submits his face” — this refers to outwardly following all the commandments of Allah the Exalted.
“And he is a doer of good (muḥsin)” — this refers to inner sincerity, or it means the first part refers to Islam and monotheism, and the second part (ihsan) refers to following the Sunnah.
“To the firmest handhold (al-‘urwah al-wuthqā)” — this is a simile: just as a person escapes from a storm or flood by holding on to a strong ring (a firm grip), similarly, salvation from Allah’s punishment, all tribulations, and misguidance comes through a path in which a person holds firmly to monotheism and the Qur’an, acts upon it fully through the Sunnah and Hadith, and uses it as his evidence.
[23,24] After describing the state of both groups, this verse offers consolation to the Messenger of Allah (May Allah bless him and give him peace) and a warning to the deniers.
“So let not (their rejection) grieve you” — the meaning is: do not grieve to the extent that you abandon your mission because they do not accept it. This is a prohibition against excessive sorrow.
As for the feeling of grief itself, which is involuntary, that cannot be prohibited.