﴿ وَقَوْمَ نُوحٍۢ لَّمَّا كَذَّبُوا۟ ٱلرُّسُلَ أَغْرَقْنَٰهُمْ وَجَعَلْنَٰهُمْ لِلنَّاسِ ءَايَةًۭ ۖ وَأَعْتَدْنَا لِلظَّٰلِمِينَ عَذَابًا أَلِيمًۭا ﴾

“And [think of] the people of Noah: when they gave the lie to [one of] the apostles, We caused them to drown, and made them a symbol for all mankind: for, grievous suffering have We readied for all who [knowingly] do wrong!”

And mention the people of Noah when they denied the messengers in denying Noah — it is as though he were many messengers given the length of time he remained among them; or it is thus expressed in the plural because to deny him is equivalent to denying all the other messengers for they all came with the same Message concerning affirmation of God’s Oneness — We drowned them this is the response to lammā ‘when’ and made them a sign a lesson for mankind thereafter and We have prepared in the Hereafter for the evildoers the disbelievers a painful chastisement in addition to what chastisement may befall them in this world.