Hadith 36, 40 Hadith an-Nawawi
On the authority of Abu Hurayrah (may Allah be pleased with him), that the Prophet (peace and blessings of Allah be upon him) said:
Whoever removes a worldly grief from a believer, Allah will remove from him one of the griefs of the Day of Resurrection. And whoever alleviates the need of a needy person, Allah will alleviate his needs in this world and the Hereafter. Whoever shields [or hides the misdeeds of] a Muslim, Allah will shield him in this world and the Hereafter. And Allah will aid His slave so long as he aids his brother. And whoever follows a path to seek knowledge therein, Allah will make easy for him a path to Paradise. No people gather together in one of the Houses of Allah, reciting the Book of Allah and studying it among themselves, except that sakeenah (tranquility) descends upon them, and mercy envelops them, and the angels surround them, and Allah mentions them amongst those who are with Him. And whoever is slowed down by his actions, will not be hastened forward by his lineage.

Related by [Muslim] in these words.
عَنْ أَبِي هُرَيْرَةَ رَضِيَ اللهُ عَنْهُ عَنْ النَّبِيِّ صلى الله عليه و سلم قَالَ: "مَنْ نَفَّسَ عَنْ مُؤْمِنٍ كُرْبَةً مِنْ كُرَبِ الدُّنْيَا نَفَّسَ اللَّهُ عَنْهُ كُرْبَةً مِنْ كُرَبِ يَوْمِ الْقِيَامَةِ، وَمَنْ يَسَّرَ عَلَى مُعْسِرٍ، يَسَّرَ اللَّهُ عَلَيْهِ فِي الدُّنْيَا وَالْآخِرَةِ، وَمَنْ سَتَرَ مُسْلِما سَتَرَهُ اللهُ فِي الدُّنْيَا وَالْآخِرَةِ ، وَاَللَّهُ فِي عَوْنِ الْعَبْدِ مَا كَانَ الْعَبْدُ فِي عَوْنِ أَخِيهِ، وَمَنْ سَلَكَ طَرِيقًا يَلْتَمِسُ فِيهِ عِلْمًا سَهَّلَ اللَّهُ لَهُ بِهِ طَرِيقًا إلَى الْجَنَّةِ، وَمَا اجْتَمَعَ قَوْمٌ فِي بَيْتٍ مِنْ بُيُوتِ اللَّهِ يَتْلُونَ كِتَابَ اللَّهِ، وَيَتَدَارَسُونَهُ فِيمَا بَيْنَهُمْ؛ إلَّا نَزَلَتْ عَلَيْهِمْ السَّكِينَةُ، وَغَشِيَتْهُمْ الرَّحْمَةُ، وَ حَفَّتهُمُ المَلاَئِكَة، وَذَكَرَهُمْ اللَّهُ فِيمَنْ عِنْدَهُ، وَمَنْ أَبَطْأَ بِهِ عَمَلُهُ لَمْ يُسْرِعْ بِهِ نَسَبُهُ". 
[رَوَاهُ مُسْلِمٌ] بهذا اللفظ.