عـن أبي حَـمـزةَ أنـسِ بـنِ مـالـكٍ رضي الله عـنـه، خــادمِ رسـولِ الله صلى الله عـلـيـه وسـلم، عن النبيِّ صلى الله عـلـيـه وسـلـم قــال: ( لا يـُؤمـنُ أحدُكم حتى يُـحِـبَّ لأخـيـه مــا يُـحِـبُّ لنفـسـِهِ) رواه البخاري ومسلم

Both Imam al-Bukhariyy and Muslim narrated from the route of Abu Hamzah Anas Ibn Malik (radiyallahu ^anhu) - the servant of the Messenger of Allah (sallallahu ^alayhi wa sallam) - that the Prophet (sallallahu ^alayhi wa sallam) said what means:
( None of you would have all the characteristics of the true believer until he loves for his brother that which he loves for himself ).
The scholars have said that the meaning of the hadith is that the one who does not have this characteristic has not achieved the perfect level of Iman, while he has already achieved the basic level of Iman.
The intended meaning of "loves for his brother" is those things which are among the acts of obedience to Allah, and the permissible matters, as opposed to the evil or Haram matters, and this is clarified from another hadith narrated by an-Nasa'iyy which mentions : "until he loves for his brother from the good that which he loves for himself".
Every believer should sympathise with his brother especially when the latter is experiencing some calamities and hardships. This meaning is understood from another hadith which states that: "The Believers are like a single body; if a single limb feels pain, then the whole body along with it suffers with fever and sleeplessness."