Surah At-Taubah, Ayat 82-83

Ayat 82. So let them laugh a little and (they will) cry much as a recompense of what they used to earn (by committing sins).

Ayat 83. If Allah brings you back to a party of them (the hypocrites), and they ask your permission to go out (to fight), say: "Never shall you go out with me, nor fight an enemy with me; you agreed to sit inactive on the first occasion, then you sit (now) with those who lag behind." 

Hazrat Anas bin Malik (May Allah be pleased with him) reported: Messenger of Allah [SAWW](PBUH) delivered a Khutbah to us the like of which I had never heard from him before. He said, "If you knew what I know, you would laugh little and weep much". Thereupon those present covered their faces and began sobbing. [Al-Bukhari Hadith # ].

Another narration is: Messenger of Allah [SAWW](PBUH) heard of something about his Companions upon which he addressed them and said, "Jannah and (Hell) Fire were shown to me and I have never seen the like of this day in good and in evil. If you were to know what I know, you would laugh little and weep much". His Companions experienced such suffering on that day that had no equal. They covered their faces and began to weep. [Al-Bukhari Hadith #].

Lesson : as mentioned above in Surah At-Taubah Ayat.82."So let them laugh a little and (they will) cry much as a recompense of what they used to earn (by committing sins)". We learn from this Hadith that Jannah and Hell do exist. The Prophet (PBUH) was shown both of them. 2. Excessive laughing is improper because it indicates that one is careless and forgetful of the Hereafter, while a Muslim is required to be all the time alert and careful about it. 3. To weep out of fear of Allah, is praiseworthy because it indicates that one's heart is full of fear and he is worried about the Hereafter.