Surah Al-Baqara, Verse 235
وَلَا جُنَاحَ عَلَيْكُمْ فِيمَا عَرَّضْتُم بِهِۦ مِنْ خِطْبَةِ ٱلنِّسَآءِ أَوْ أَكْنَنتُمْ فِىٓ أَنفُسِكُمْ ۚ عَلِمَ ٱللَّهُ أَنَّكُمْ سَتَذْكُرُونَهُنَّ وَلَٰكِن لَّا تُوَاعِدُوهُنَّ سِرًّا إِلَّآ أَن تَقُولُوا۟ قَوْلًۭا مَّعْرُوفًۭا ۚ وَلَا تَعْزِمُوا۟ عُقْدَةَ ٱلنِّكَاحِ حَتَّىٰ يَبْلُغَ ٱلْكِتَٰبُ أَجَلَهُۥ ۚ وَٱعْلَمُوٓا۟ أَنَّ ٱللَّهَ يَعْلَمُ مَا فِىٓ أَنفُسِكُمْ فَٱحْذَرُوهُ ۚ وَٱعْلَمُوٓا۟ أَنَّ ٱللَّهَ غَفُورٌ حَلِيمٌۭ
Translation — Sahih International
There is no blame upon you for that to which you [indirectly] allude concerning a proposal to women or for what you conceal within yourselves. Allah knows that you will have them in mind. But do not promise them secretly except for saying a proper saying. And do not determine to undertake a marriage contract until the decreed period reaches its end. And know that Allah knows what is within yourselves, so beware of Him. And know that Allah is Forgiving and Forbearing.
Source
Kur'an-ı Kerim, Bakara Suresi 2:235
https://kuran.diyanet.gov.tr/mushaf/kuran-meal-2/2-suresi-235-ayet