Hadith 2, 40 Hadith an-Nawawi
Also on the authority of `Umar (ra) who said:
While we were one day sitting with the Messenger of Allah (ﷺ) there appeared before us a man dressed in extremely white clothes and with very black hair. No traces of journeying were visible on him, and none of us knew him.

He sat down close by the Prophet (ﷺ) rested his knees against the knees of the Prophet (ﷺ) and placed his palms over his thighs, and said: "O Muhammad! Inform me about Islam." The Messenger of Allah (ﷺ) replied: "Islam is that you should testify that there is no deity worthy of worship except Allah and that Muhammad is His Messenger (ﷺ), that you should perform salah (ritual prayer), pay the zakah, fast during Ramadan, and perform Hajj (pilgrimage) to the House (the Ka`bah at Makkah), if you can find a way to it (or find the means for making the journey to it)." He said: "You have spoken the truth."

We were astonished at his thus questioning him (ﷺ) and then telling him that he was right, but he went on to say, "Inform me about Iman (faith)." He (the Prophet) answered, "It is that you believe in Allah and His angels and His Books and His Messengers and in the Last Day, and in fate (qadar), both in its good and in its evil aspects." He said, "You have spoken the truth."

Then he (the man) said, "Inform me about Ihsan." He (the Prophet) answered, "It is that you should serve Allah as though you could see Him, for though you cannot see Him yet He sees you."

He said, "Inform me about the Hour." He (the Prophet) said, "About that the one questioned knows no more than the questioner." So he said, "Well, inform me about its signs." He said, "They are that the slave-girl will give birth to her mistress and that you will see the barefooted ones, the naked, the destitute, the herdsmen of the sheep (competing with each other) in raising lofty buildings." Thereupon the man went off.

I waited a while, and then he (the Prophet) said, "O `Umar, do you know who that questioner was?" I replied, "Allah and His Messenger know better." He said, "That was Jibril. He came to teach you your religion."

[ Muslim ]
عَنْ عُمَرَ رَضِيَ اللهُ عَنْهُ أَيْضًا قَالَ: " بَيْنَمَا نَحْنُ جُلُوسٌ عِنْدَ رَسُولِ اللَّهِ صلى الله عليه و سلم ذَاتَ يَوْمٍ، إذْ طَلَعَ عَلَيْنَا رَجُلٌ شَدِيدُ بَيَاضِ الثِّيَابِ، شَدِيدُ سَوَادِ الشَّعْرِ، لَا يُرَى عَلَيْهِ أَثَرُ السَّفَرِ، وَلَا يَعْرِفُهُ مِنَّا أَحَدٌ. حَتَّى جَلَسَ إلَى النَّبِيِّ صلى الله عليه و سلم . فَأَسْنَدَ رُكْبَتَيْهِ إلَى رُكْبَتَيْهِ، وَوَضَعَ كَفَّيْهِ عَلَى فَخِذَيْهِ، 
وَقَالَ: يَا مُحَمَّدُ أَخْبِرْنِي عَنْ الْإِسْلَامِ. 
فَقَالَ رَسُولُ اللَّهِ صلى الله عليه و سلم الْإِسْلَامُ أَنْ تَشْهَدَ أَنْ لَا إلَهَ إلَّا اللَّهُ وَأَنَّ مُحَمَّدًا رَسُولُ اللَّهِ، وَتُقِيمَ الصَّلَاةَ، وَتُؤْتِيَ الزَّكَاةَ، وَتَصُومَ رَمَضَانَ، وَتَحُجَّ الْبَيْتَ إنْ اسْتَطَعْت إلَيْهِ سَبِيلًا. 
قَالَ: صَدَقْت . فَعَجِبْنَا لَهُ يَسْأَلُهُ وَيُصَدِّقُهُ!
قَالَ: فَأَخْبِرْنِي عَنْ الْإِيمَانِ. 
قَالَ: أَنْ تُؤْمِنَ بِاَللَّهِ وَمَلَائِكَتِهِ وَكُتُبِهِ وَرُسُلِهِ وَالْيَوْمِ الْآخِرِ، وَتُؤْمِنَ بِالْقَدَرِ خَيْرِهِ وَشَرِّهِ.
قَالَ: صَدَقْت. قَالَ: فَأَخْبِرْنِي عَنْ الْإِحْسَانِ. 
قَالَ: أَنْ تَعْبُدَ اللَّهَ كَأَنَّك تَرَاهُ، فَإِنْ لَمْ تَكُنْ تَرَاهُ فَإِنَّهُ يَرَاك. 
قَالَ: فَأَخْبِرْنِي عَنْ السَّاعَةِ. قَالَ: مَا الْمَسْئُولُ عَنْهَا بِأَعْلَمَ مِنْ السَّائِلِ. 
قَالَ: فَأَخْبِرْنِي عَنْ أَمَارَاتِهَا؟ قَالَ: أَنْ تَلِدَ الْأَمَةُ رَبَّتَهَا، وَأَنْ تَرَى الْحُفَاةَ الْعُرَاةَ الْعَالَةَ رِعَاءَ الشَّاءِ يَتَطَاوَلُونَ فِي الْبُنْيَانِ. ثُمَّ انْطَلَقَ، فَلَبِثْتُ مَلِيًّا، 
ثُمَّ قَالَ: يَا عُمَرُ أَتَدْرِي مَنْ السَّائِلُ؟. 
‫‬قُلْتُ: اللَّهُ وَرَسُولُهُ أَعْلَمُ. 
قَالَ: فَإِنَّهُ جِبْرِيلُ أَتَاكُمْ يُعَلِّمُكُمْ دِينَكُمْ ". [رَوَاهُ مُسْلِمٌ]
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