The etiquette of friendship are: to give [your friend] preference in your wealth, or, if you cannot do this, to give freely out of your surplus wealth when he is in need; to provide swift assistance when he is in need, in person and without his having to request it; to keep his secrets; to conceal his faults; not to pass on people’s criticism of him that would upset him; to pass on people's praise of him that would please him; to pay full attention when he speaks; not to pick apart his words [in argumentation]; to call him by the names he likes most; to praise him for what you know or his praiseworthy traits; to thank him for the favors he does for you; to defend him in his absence from all infringements upon his honor as you would defend yourself; to give him advice with gentleness and by subtle hints if he needs it; to pardon his slips and errors, and not to censure him; to pray for him in the ritual prayer, during his life and after his death; to remain loyal to his family and relatives after his death; to choose to make things easy for him by not burdening him with any of your own needs, so as to keep his heart free from your concerns; to express joy at all the happy оссаsions in his life and sadness at all calamities that afflict him; to be in your innermost heart just as you appear outwardly, so that you are truly sincere in your love for him, in private and in public; to be the one who initiates the greeting of peace when you meet him; to make room for him to sit in a gathering; to come out of the house to welcome him; to see him off when he leaves; to keep quiet while he is talking until he finishes, and to refrain from interrupting him.
In short, you should treat your friend exactly as you would like to be treated. For truly, the brotherhood of a person who does not love for his brother what he loves for himself is mere hypocrisy and will have evil consequences for him both in this world and the Hereafter. These are the courtesies due to people in general that you do not know, and to those close friends who are your brothers.
وَبِالْوَالِدَيْنِ إِحْسَانًا
"And to parents, good treatment."