Muwatta Malik, Book 17, Hadith 6 (USC-MSA)

Yahya related to me from Malik from Nafi that Abdullah ibn Umar used to say, "Zakat does not have to be paid on property until a year has elapsed over it."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَقُولُ ‏:‏ لاَ تَجِبُ فِي مَالٍ زَكَاةٌ حَتَّى يَحُولَ عَلَيْهِ الْحَوْلُ ‏.‏

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also referenced under: Book 17, Hadith 586 (In-Book)