One ayat is in Quran Chapter Ali Imran (Chapter 3) verse 103:
"And hold firmly to the rope of Allah all together and do not become divided. And remember the favor of Allah upon you - when you were enemies and He brought your hearts together and you became, by His favor, brothers. And you were on the edge of a pit of the Fire, and He saved you from it. Thus does Allah make clear to you His verses that you may be guided."
One hadith/tradition of the Prophet is:
“The believers, in their mutual mercy, love and compassion, are like a (single) body; if one part of it feels pain, the rest of the body will join it in staying awake and suffering fever.” (Narrated by al-Bukhaari)