'Abdu'r-Rahman ibn Ziyad ibn An'am al-Ifriqi said, "My father toldme that they were taking part in a sea raid in the time of Mu'awiya. Hesaid, 'Our ship was right up against the ship of Abu Ayyub al-Ansari. Whenit was time for our midday meal, we invited him and he came over. He said,"You invited me, but even though I am fasting, I cannot avoid acceptingyour invitation because I heard the Messenger of Allah, may Allah blesshim and grant him peace, say, 'A Muslim owes six things to his brother.If he neglects any of them, he has neglected an obligatory duty owed tohis brother. He should return his greeting when he greets him. He shouldaccept when he gives him an invitation. He should ask for mercy on himwhen he sneezes. He should give him good counsel when he asks him for advice.'"'"
English reference: Book 40, Hadith 922
Arabic reference: Book 1, Hadith 922