مُوَطَّأُ مَالِكٍ
Muwatta Malik 586
Zakat
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَقُولُ : لاَ تَجِبُ فِي مَالٍ زَكَاةٌ حَتَّى يَحُولَ عَلَيْهِ الْحَوْلُ .
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."
Arabic/English book reference: Book 17, Hadith 6