Sahih al-Bukhari Book 46, Hadith 7
The Prophet (ﷺ) said, "A believer to another believer is like a building whose different parts enforce each
other." The Prophet (ﷺ) then clasped his hands with the fingers interlaced (while saying that).
I heard Al-Bara' bin `Azib saying, "The Prophet (ﷺ) orders us to do seven things and prohibited us from doing seven other things." Then Al-Bara' mentioned the following:-- (1) To pay a visit to the sick (inquiring about his health), (2) to follow funeral processions, (3) to say to a sneezer, "May Allah be merciful to you" (if he says, "Praise be to Allah!"), (4) to return greetings, (5) to help the oppressed, (6) to accept invitations, (7) to help others to fulfill their oaths. (See Hadith No. 753, Vol. 7)
The Prophet (ﷺ) said, "Oppression will be a darkness on the Day of Resurrection."