(It is permissible) to look at a woman before marrying.

Narrated Sahl bin Sad:

A woman came to Allah's Apostle ﷺ and said, "O Allah's Apostle! I have come to you to present myself to you (for marriage)." Allah's Apostle glanced at her. He looked at her carefully and fixed his glance on her and then lowered his head. When the lady saw that he did not say anything, she sat down. A man from his companions got up and said, "O Allah's Apostle! If you are not in need of her, then marry her to me." The Prophet ﷺ said, "Have you got anything to offer." The man said, 'No, by Allah, O Allah's Apostle!" The Prophet ﷺ said (to him), "Go to your family and try to find something." So the man went and returned, saying, "No, by Allah, O Allah's Apostle! I have not found anything." The Prophet ﷺ said, "Go again and look for something, even if it were an iron ring." He went and returned, saying, "No, by Allah, O Allah's Apostle! I could not find even an iron ring, but this is my Izar (waist sheet).' He had no Rida (upper garment). He added, "I give half of it to her." Allah's Apostle ﷺ said "What will she do with your Izar? If you wear it, she will have nothing over herself thereof (will be naked),
and if she wears it, then you will have nothing over yourself thereof ' So the man sat for a long period and then got up (to leave). When Allah's Apostle saw him leaving, he ordered that he be called back. When he came, the Prophet asked (him), "How much of the Qur'an do you know (by heart)?" The man replied, I know such Surah and such Surah and such Surah," naming the surahs. The Prophet ﷺ said, "Can you recite it by heart?" He said, 'Yes." The Prophet ﷺ said, "Go I let you marry her for what you know of the Quran (as her Mahr).

حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا يَعْقُوبُ، عَنْ أَبِي حَازِمٍ، عَنْ سَهْلِ بْنِ سَعْدٍ، أَنَّ امْرَأَةً، جَاءَتْ رَسُولَ اللَّهِ ﷺ فَقَالَتْ يَا رَسُولَ اللَّهِ جِئْتُ لأَهَبَ لَكَ نَفْسِي. فَنَظَرَ إِلَيْهَا رَسُولُ اللَّهِ ﷺ فَصَعَّدَ النَّظَرَ إِلَيْهَا وَصَوَّبَهُ، ثُمَّ طَأْطَأَ رَأْسَهُ، فَلَمَّا رَأَتِ الْمَرْأَةُ أَنَّهُ لَمْ يَقْضِ فِيهَا شَيْئًا جَلَسَتْ، فَقَامَ رَجُلٌ مِنْ أَصْحَابِهِ فَقَالَ أَىْ رَسُولَ اللَّهِ إِنْ لَمْ تَكُنْ لَكَ بِهَا حَاجَةٌ فَزَوِّجْنِيهَا. فَقَالَ " هَلْ عِنْدَكَ مِنْ شَىْءٍ ". قَالَ لاَ وَاللَّهِ يَا رَسُولَ اللَّهِ. قَالَ " اذْهَبْ إِلَى أَهْلِكَ فَانْظُرْ هَلْ تَجِدُ شَيْئًا ". فَذَهَبَ ثُمَّ رَجَعَ فَقَالَ لاَ وَاللَّهِ يَا رَسُولَ اللَّهِ مَا وَجَدْتُ شَيْئًا. قَالَ " انْظُرْ وَلَوْ خَاتَمًا مِنْ حَدِيدٍ ". فَذَهَبَ ثُمَّ رَجَعَ فَقَالَ لاَ وَاللَّهِ يَا رَسُولَ اللَّهِ وَلاَ خَاتَمًا مِنْ حَدِيدٍ، وَلَكِنْ هَذَا إِزَارِي ـ قَالَ سَهْلٌ مَا لَهُ رِدَاءٌ ـ فَلَهَا نِصْفُهُ. فَقَالَ رَسُولُ اللَّهِ ﷺ " مَا تَصْنَعُ بِإِزَارِكَ إِنْ لَبِسْتَهُ لَمْ يَكُنْ عَلَيْهَا مِنْهُ شَىْءٌ، وَإِنْ لَبِسَتْهُ لَمْ يَكُنْ عَلَيْكَ شَىْءٌ ". فَجَلَسَ الرَّجُلُ حَتَّى طَالَ مَجْلَسُهُ ثُمَّ قَامَ فَرَآهُ رَسُولُ اللَّهِ ﷺ مُوَلِّيًا فَأَمَرَ بِهِ فَدُعِيَ فَلَمَّا جَاءَ قَالَ " مَاذَا مَعَكَ مِنَ الْقُرْآنِ ". قَالَ مَعِي سُورَةَ كَذَا وَسُورَةَ كَذَا وَسُورَةَ كَذَا. عَدَّدَهَا. قَالَ " أَتَقْرَؤُهُنَّ عَنْ ظَهْرِ قَلْبِكَ ". قَالَ نَعَمْ. قَالَ " اذْهَبْ فَقَدْ مَلَّكْتُكَهَا بِمَا مَعَكَ مِنَ الْقُرْآنِ ".