Malik bin Aws narrates: Once we were sitting with Sayyiduna Uthman Ghani (may Allah be pleased with him), when Sayyiduna Abu Dharr Ghifari (may Allah be pleased with him) came to him and greeted him with salam. Sayyiduna Uthman (may Allah be pleased with him) asked him: "O Abu Dharr! How are you?" He replied: "I am fine." Then he went and stood by a pillar, and the people also got up and went towards him and surrounded him. I was also among those who surrounded him. The people said: "O Abu Dharr! Narrate to us a hadith from the Prophet (peace and blessings be upon him)." So he said: I heard the Prophet (peace and blessings be upon him) say: "Zakat is obligatory on camels, zakat is obligatory on goats, zakat is obligatory on cows, and zakat is obligatory on linen (silk)." The narrator says: He mentioned this word with the letter 'z'.