The Quran root ط م أ ن ṭ-m-’-n

وَإِذْ قَالَ إِبْرَاهِيمُ رَبِّ أَرِنِي كَيْفَ تُحْيِي الْمَوْتَىٰ قَالَ أَوَلَمْ تُؤْمِن قَالَ بَلَىٰ وَلَٰكِن لِّيَطْمَئِنَّ قَلْبِي قَالَ فَخُذْ أَرْبَعَةً مِّنَ الطَّيْرِ فَصُرْهُنَّ إِلَيْكَ ثُمَّ اجْعَلْ عَلَىٰ كُلِّ جَبَلٍ مِّنْهُنَّ جُزْءًا ثُمَّ ادْعُهُنَّ يَأْتِينَكَ سَعْيًا وَاعْلَمْ أَنَّ اللَّهَ عَزِيزٌ حَكِيمٌ ٢٦٠

لِّيَطْمَئِنَّ liyaṭma-inna · to satisfy

And [mention] when Abraham said, "My Lord, show me how You give life to the dead." [Allāh] said, "Have you not believed?" He said, "Yes, but [I ask] only that my heart may be satisfied." [Allāh] said, "Take four birds and commit them to yourself. Then [after slaughtering them] put on each hill a portion of them; then call them - they will come [flying] to you in haste. And know that Allāh is Exalted in Might and Wise." (Surah Al-Baqarah, 2:260)

وَمَا جَعَلَهُ اللَّهُ إِلَّا بُشْرَىٰ لَكُمْ وَلِتَطْمَئِنَّ قُلُوبُكُم بِهِ وَمَا النَّصْرُ إِلَّا مِنْ عِندِ اللَّهِ الْعَزِيزِ الْحَكِيمِ ١٢٦

وَلِتَطْمَئِنَّ walitaṭma-inna · and to reassure

And Allāh made it not except as [a sign of] good tidings for you and to reassure your hearts thereby. And victory is not except from Allāh, the Exalted in Might, the Wise - (Surah Ali 'Imran, 3:126)

مَن كَفَرَ بِاللَّهِ مِن بَعْدِ إِيمَانِهِ إِلَّا مَنْ أُكْرِهَ وَقَلْبُهُ مُطْمَئِنٌّ بِالْإِيمَانِ وَلَٰكِن مَّن شَرَحَ بِالْكُفْرِ صَدْرًا فَعَلَيْهِمْ غَضَبٌ مِّنَ اللَّهِ وَلَهُمْ عَذَابٌ عَظِيمٌ ١٠٦

مُطْمَئِنٌّ muṭ'ma-innun · (is) content

Whoever disbelieves in [i.e., denies] Allāh after his belief... except for one who is forced [to renounce his religion] while his heart is secure in faith. But those who [willingly] open their breasts to disbelief, upon them is wrath from Allāh, and for them is a great punishment; (Surah An-Nahl, 16:106)

وَضَرَبَ اللَّهُ مَثَلًا قَرْيَةً كَانَتْ آمِنَةً مُّطْمَئِنَّةً يَأْتِيهَا رِزْقُهَا رَغَدًا مِّن كُلِّ مَكَانٍ فَكَفَرَتْ بِأَنْعُمِ اللَّهِ فَأَذَاقَهَا اللَّهُ لِبَاسَ الْجُوعِ وَالْخَوْفِ بِمَا كَانُوا يَصْنَعُونَ ١١٢

مُّطْمَئِنَّةً muṭ'ma-innatan · and content

And Allāh presents an example: a city [i.e., Makkah] which was safe and secure, its provision coming to it in abundance from every location, but it denied the favors of Allāh. So Allāh made it taste the envelopment of hunger and fear for what they had been doing. (Surah An-Nahl, 16:112)