Uthman bin al-Aswad (may Allah have mercy on him) says: One of those who used to sit with Sayyiduna Ibn Abbas (may Allah be pleased with them both) told us: Sayyiduna Ibn Abbas (may Allah be pleased with them both) said to me: Where have you come from? I said: I have drunk Zamzam. He said: Did you drink it as it ought to be drunk? I said: How should I drink? He said: When you drink, face the Qiblah, then mention the name of Allah, then take three breaths and drink your fill; and when you have finished, praise Allah, for the Prophet (peace and blessings be upon him) said: "The sign between us and the hypocrites is that they do not drink their fill of Zamzam."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9656