It is narrated from Sayyiduna al-Sa'ib (may Allah be pleased with him) that he used to say: "Drink from the siqayah of Sayyiduna al-Abbas (may Allah be pleased with him) (the arrangement for giving water to the pilgrims), for it is part of the Sunnah."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6591