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Surah 15. Al-Hijr
Ayah 10 - 13
10 وَلَقَدْ أَرْسَلْنَا مِن قَبْلِكَ فِى شِيَعِ ٱلْأَوَّلِينَ
11 وَمَا يَأْتِيهِم مِّن رَّسُولٍ إِلَّا كَانُوا۟ بِهِۦ يَسْتَهْزِءُونَ
12 كَذَٰلِكَ نَسْلُكُهُۥ فِى قُلُوبِ ٱلْمُجْرِمِينَ
13 لَا يُؤْمِنُونَ بِهِۦ ۖ وَقَدْ خَلَتْ سُنَّةُ ٱلْأَوَّلِينَ
10. Indeed, We sent (Messengers) before you (O Muhammad) amongst the earlier communities. 11. And there never came a Messenger to them but that they mocked him. 12. Thus We allow it to enter the hearts of the guilty. 13. They would not believe in it (the Qur'an); and already the example of the ancients has gone forth.
Consoling His Messenger for the rejection of the disbelieving Quraysh, Allah says that He has sent Messengers before him to the nations of the past, and no Messenger came to a nation but they rejected him and mocked him. Then He tells him that He lets disbelief enter the hearts of those sinners who are too stubborn and too arrogant to follow His guidance.
(Thus We allow it to enter the hearts of the guilty.) Anas and Al-Hasan Al-Basri said that this referred to Shirk.
(and already the example of the ancients has gone forth.) meaning the destruction wrought by Allah on those who rejected His Messengers, and how He saved His Prophets and their followers in this world and in the Hereafter, is well known.