I know (about) the Hijab (the order of veiling of women) more than anybody else. Ubai bin Kaʿb used to ask me about it. Messenger of Allah ﷺ became the bridegroom of Zainab bint Jahsh whom he married at Medina. After the sun had risen high in the sky, the Prophet ﷺ invited the people to a meal. Allah's Apostle remained sitting and some people remained sitting with him after the other guests had left. Then Messenger of Allah ﷺ got up and went away, and I too, followed him till he reached the door of ʿAisha's room. Then he thought that the people must have left the place by then, so he returned and I also returned with him. Behold, the people were still sitting at their places. So he went back again for the second time, and I went along with him too. When we reached the door of ʿAisha's room, he returned and I also returned with him to see that the people had left. Thereupon the Prophet ﷺ hung a curtain between me and him and the Verse regarding the order for (veiling of women) Hijab was revealed.  

أَنَا أَعْلَمُ النَّاسِ بِالْحِجَابِ كَانَ أُبَىُّ بْنُ كَعْبٍ يَسْأَلُنِي عَنْهُ أَصْبَحَ رَسُولُ اللَّهِ ﷺ عَرُوسًا بِزَيْنَبَ ابْنَةِ جَحْشٍ وَكَانَ تَزَوَّجَهَا بِالْمَدِينَةِ فَدَعَا النَّاسَ لِلطَّعَامِ بَعْدَ ارْتِفَاعِ النَّهَارِ فَجَلَسَ رَسُولُ اللَّهِ ﷺ وَجَلَسَ مَعَهُ رِجَالٌ بَعْدَ مَا قَامَ الْقَوْمُ حَتَّى قَامَ رَسُولُ اللَّهِ ﷺ فَمَشَى وَمَشَيْتُ مَعَهُ حَتَّى بَلَغَ باب حُجْرَةِ عَائِشَةَ ثُمَّ ظَنَّ أَنَّهُمْ خَرَجُوا فَرَجَعْتُ مَعَهُ فَإِذَا هُمْ جُلُوسٌ مَكَانَهُمْ فَرَجَعَ وَرَجَعْتُ مَعَهُ الثَّانِيَةَ حَتَّى بَلَغَ باب حُجْرَةِ عَائِشَةَ فَرَجَعَ وَرَجَعْتُ مَعَهُ فَإِذَا هُمْ قَامُوا فَضَرَبَ بَيْنِي وَبَيْنَهُ سِتْرًا وَأُنْزِلَ الْحِجَابُ  

I was the best informed among the people pertaining to Hijab (veil and seclusion). Ubayy b. Ka'b used to ask me about it. Anas (Allah be pleased with him) thus narrated: The Messenger of Allah ﷺ got up in the morning as a bridegroom of Zainab bint jahsh (Allah be pleased witt her) as he had married her at Medina. He invited people to the wedding feast after the day had well risen. There sat Messenger of Allah ﷺ and there kept sitting along with him some persons after the people had stood up (for departure) ; then Messenger of Allah ﷺ stood up and walked on and I also walked along with him until he reached the door of the apartment of 'A'isha (Allah be pleased with her). He then thought that they (those who had been sitting there after meal) had gone away. So he returned and I also returned with him, but they were still sitting at their places. So he returned for the second time and I also returned until he reached the apartment of 'A'isha. He again returned and I also returned and they had (by that time) stood up, and he hung a curtain between me and him (at the door of the apartment of Hadrat Zainab, where he had to stay), and Allah revealed the verse pertaining to veil.  

أَنَسٌ أَصْبَحَ رَسُولُ اللَّهِ ﷺ عَرُوسًا بِزَيْنَبَ بِنْتِ جَحْشٍ قَالَ وَكَانَ تَزَوَّجَهَا بِالْمَدِينَةِ فَدَعَا النَّاسَ لِلطَّعَامِ بَعْدَ ارْتِفَاعِ النَّهَارِ فَجَلَسَ رَسُولُ اللَّهِ ﷺ وَجَلَسَ مَعَهُ رِجَالٌ بَعْدَ مَا قَامَ الْقَوْمُ حَتَّى قَامَ رَسُولُ اللَّهِ ﷺ فَمَشَى فَمَشَيْتُ مَعَهُ حَتَّى بَلَغَ بَابَ حُجْرَةِ عَائِشَةَ ثُمَّ ظَنَّ أَنَّهُمْ قَدْ خَرَجُوا فَرَجَعَ وَرَجَعْتُ مَعَهُ فَإِذَا هُمْ جُلُوسٌ مَكَانَهُمْ فَرَجَعَ فَرَجَعْتُ الثَّانِيَةَ حَتَّى بَلَغَ حُجْرَةَ عَائِشَةَ فَرَجَعَ فَرَجَعْتُ فَإِذَا هُمْ قَدْ قَامُوا فَضَرَبَ بَيْنِي وَبَيْنَهُ بِالسِّتْرِ وَأَنْزَلَ اللَّهُ آيَةَ الْحِجَابِ  

I was the best informed among the people pertaining to Hijab (veil and seclusion). Ubayy b. Ka'b used to ask me about it. Anas (Allah be pleased with him) thus narrated: The Messenger of Allah ﷺ got up in the morning as a bridegroom of Zainab bint jahsh (Allah be pleased witt her) as he had married her at Medina. He invited people to the wedding feast after the day had well risen. There sat Messenger of Allah ﷺ and there kept sitting along with him some persons after the people had stood up (for departure) ; then Messenger of Allah ﷺ stood up and walked on and I also walked along with him until he reached the door of the apartment of 'A'isha (Allah be pleased with her). He then thought that they (those who had been sitting there after meal) had gone away. So he returned and I also returned with him, but they were still sitting at their places. So he returned for the second time and I also returned until he reached the apartment of 'A'isha. He again returned and I also returned and they had (by that time) stood up, and he hung a curtain between me and him (at the door of the apartment of Hadrat Zainab, where he had to stay), and Allah revealed the verse pertaining to veil. (Using translation from Muslim 1428f)  

عَنْهُ قَالَ أَنَسٌ أَصْبَحَ رَسُولُ اللهِ ﷺ عَرُوسًا بِزَيْنَبَ ابْنَةِ جَحْشٍ قَالَ وَكَانَ تَزَوَّجَهَا بِالْمَدِينَةِ فَدَعَا النَّاسَ لِلطَّعَامِ بَعْدَ ارْتِفَاعِ النَّهَارِ فَجَلَسَ رَسُولُ اللهِ ﷺ وَجَلَسَ مَعَهُ رِجَالٌ بَعْدَمَا قَامَ الْقَوْمُ حَتَّى قَامَ رَسُولُ اللهِ ﷺ فَمَشَى وَمَشَيْتُ مَعَهُ حَتَّى بَلَغَ حُجْرَةَ عَائِشَةَ ثُمَّ ظَنَّ أَنَّهُمْ قَدْ خَرَجُوا فَرَجَعَ وَرَجَعْتُ مَعَهُ قَالَ فَإِذَا هُمْ جُلُوسٌ مَكَانَهُمْ فَرَجَعَ وَرَجَعْتُ مَعَهُ الثَّانِيَةَ حَتَّى بَلَغَ حُجْرَةَ عَائِشَةَ فَرَجَعَ وَرَجَعْتُ مَعَهُ فَإِذَا هُمْ قَدْ قَامُوا فَضَرَبَ بَيْنِي وَبَيْنَهُ بِالسِّتْرِ وَأُنْزِلَالْحِجَابُ  

[Machine] Anas said, "The Messenger of Allah ﷺ became married to Zainab bint Jahsh in Al-Madinah. He invited people for a meal after the morning prayer. The Messenger of Allah ﷺ and some men sat down after the people had stood up, until the Messenger of Allah ﷺ got up and left. I walked with him until he reached the door of Aisha's room. He thought that they had left, so he returned and I returned with him. Then we found the people had stood up, so he struck a screen between me and him, and the verse of Hijab was revealed."  

أَنَسٌ «أَصْبَحَ رَسُولُ اللهِ ﷺ عَرُوسًا بِزَيْنَبَ بِنْتِ جَحْشٍ وَكَانَ تَزَوَّجَهَا بِالْمَدِينَةِ فَدَعَى النَّاسَ لِلطَّعَامِ بَعْدَ ارْتِفَاعِ النَّهَارِ فَجَلَسَ رَسُولُ اللهِ ﷺ وَجَلَسَ مَعَهُ رِجَالٌ بَعْدَ مَا قَامَ الْقَوْمُ حَتَّى قَامَ رَسُولُ اللهِ ﷺ فَمَشَى وَمَشَيْتُ مَعَهُ حَتَّى بَلَغَ بَابَ حُجْرَةِ عَائِشَةَ ثُمَّ ظَنَّ أَنَّهُمْ قَدْ خَرَجُوا فَرَجَعَ وَرَجَعْتُ مَعَهُ فَإِذَا هُمْ قَدْ قَامُوا فَضَرَبَ بَيْنِي وَبَيْنَهُ بِالسِّتْرِ وَنَزَلَتْ آيَةُ الْحِجَابِ»