Some men amongst the companions of the Prophet ﷺ were shown in their dreams that the night of Qadr was in the last seven nights of Ramadan. Messenger of Allah ﷺ said, "It seems that all your dreams agree that (the Night of Qadr) is in the last seven nights, and whoever wants to search for it (i.e. the Night of Qadr) should search in the last seven (nights of Ramadan).  

أَنَّ رِجَالاً مِنْ أَصْحَابِ النَّبِيِّ ﷺ أُرُوا لَيْلَةَ الْقَدْرِ فِي الْمَنَامِ فِي السَّبْعِ الأَوَاخِرِ فَقَالَ رَسُولُ اللَّهِ ﷺ أَرَى رُؤْيَاكُمْ قَدْ تَوَاطَأَتْ فِي السَّبْعِ الأَوَاخِرِ فَمَنْ كَانَ مُتَحَرِّيَهَا فَلْيَتَحَرَّهَا فِي السَّبْعِ الأَوَاخِرِ  

I asked Abu Saʿid, and he was a friend of mine, (about the Night of Qadr) and he said, "We practiced Iʿtikaf (seclusion in the mosque) in the middle third of the month of Ramadan with the Prophet ﷺ . In the morning of the 20th of Ramadan, the Prophet ﷺ came and addressed us and said, 'I was informed of (the date of the Night of Qadr) but I was caused to forget it; so search for it in the odd nights of the last ten nights of the month of Ramadan. (In the dream) I saw myself prostrating in mud and water (as a sign). So, whoever was in Iʿtikaf with me should return to it with me (for another 10-day's period)', and we returned. At that time there was no sign of clouds in the sky but suddenly a cloud came and it rained till rainwater started leaking through the roof of the mosque which was made of date-palm leaf stalks. Then the prayer was established and I saw Messenger of Allah ﷺ prostrating in mud and water and I saw the traces of mud on his forehead."  

سَأَلْتُ أَبَا سَعِيدٍ وَكَانَ لِي صَدِيقًا فَقَالَ اعْتَكَفْنَا مَعَ النَّبِيِّ ﷺ الْعَشْرَ الأَوْسَطَ مِنْ رَمَضَانَ فَخَرَجَ صَبِيحَةَ عِشْرِينَ فَخَطَبَنَا وَقَالَ إِنِّي أُرِيتُ لَيْلَةَ الْقَدْرِ ثُمَّ أُنْسِيتُهَا أَوْ نُسِّيتُهَا فَالْتَمِسُوهَا فِي الْعَشْرِ الأَوَاخِرِ فِي الْوَتْرِ وَإِنِّي رَأَيْتُ أَنِّي أَسْجُدُ فِي مَاءٍ وَطِينٍ فَمَنْ كَانَ اعْتَكَفَ مَعَ رَسُولِ اللَّهِ ﷺ فَلْيَرْجِعْ فَرَجَعْنَا وَمَا نَرَى فِي السَّمَاءِ قَزَعَةً فَجَاءَتْ سَحَابَةٌ فَمَطَرَتْ حَتَّى سَالَ سَقْفُ الْمَسْجِدِ وَكَانَ مِنْ جَرِيدِ النَّخْلِ وَأُقِيمَتِ الصَّلاَةُ فَرَأَيْتُ رَسُولَ اللَّهِ ﷺ يَسْجُدُ فِي الْمَاءِ وَالطِّينِ حَتَّى رَأَيْتُ أَثَرَ الطِّينِ فِي جَبْهَتِهِ