Nafi' narrates from Sayyiduna Ibn Umar (may Allah be pleased with them both): "Those who are partners shall settle the zakah share between themselves equally." Sufyan said: I said to Ubaydullah: What is meant by al-khalitayn (the two partners)? He said: Those whose pen is one, whose shepherd is one and whose bucket is also one.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7334