A believer is like a brick for another believer, the one supporting the other.  

قَالَ رَسُولُ اللَّهِ ﷺ الْمُؤْمِنُ لِلْمُؤْمِنِ كَالْبُنْيَانِ يَشُدُّ بَعْضُهُ بَعْضًا  

the Messenger of Allah ﷺ said, "The similitude of believers in their mutual love, mercy, and affection is that of one body: when any limb of it aches, the whole body aches because of sleeplessness and fever."  

قَالَ رَسُولُ اللَّهِ ﷺ: «مَثَلُ الْمُؤْمِنِينَ فِي تَوَادِّهِمْ وَتَرَاحُمِهِمْ وَتَعَاطُفِهِمْ مَثَلُ الْجَسَدِ إِذَا اشْتَكَى مِنْهُ عُضْوٌ تَدَاعَى لَهُ سَائِرُ الْجَسَدِ بِالسَّهَرِ وَالْحُمَّى۔»  

Nu'man b. Bashir reported a hadith like this from Allah's Apostle ﷺ.  

عَنِ النَّبِيِّ ﷺ بِنَحْوِهِ  

The believers are like one person; if his head aches, the whole body aches with fever and sleeplessness.  

قَالَ رَسُولُ اللَّهِ ﷺ الْمُؤْمِنُونَ كَرَجُلٍ وَاحِدٍ إِنِ اشْتَكَى رَأْسُهُ تَدَاعَى لَهُ سَائِرُ الْجَسَدِ بِالْحُمَّى وَالسَّهَرِ  

Nu'man b. Bashir reported that Muslims are like one body of a person; if the eye is sore, the whole body aches, and if the head aches, the whole body aches.  

قَالَ رَسُولُ اللَّهِ ﷺ الْمُسْلِمُونَ كَرَجُلٍ وَاحِدٍ إِنِ اشْتَكَى عَيْنُهُ اشْتَكَى كُلُّهُ وَإِنِ اشْتَكَى رَأْسُهُ اشْتَكَى كُلُّهُ  

A hadith like this has been narrated on the authority of Nu'man b. Bashir through another chain of transmitters.  

عَنِ النَّبِيِّ ﷺ نَحْوَهُ