Khalid bin Aslam reported,
We went out with Abdullah bin Umar, and an Arabi said to him, "Tell me about the words of Allah, 'And those who hoard gold and silver and do not spend it in the way of Allah' [Tawbah 9:34]."Ibn Umar replied, "Whoever hoards it and does not pay its zakat, woe to him. But this was only before zakat was revealed. When it was revealed, Allah made it a means of purifying wealth."
Azami 12456
Sahihعن خالد بن أسلم قال
خرجنا مع عبد الله بن عمر، فقال أعرابي: أخبرني قول الله {والذين يكنزون الذهب والفضة ولا ينفقونها في سبيل الله} قال ابن عمر: من كنزها، فلم يؤد زكاتها، فويل له، إنما كان هذا قبل أن تنزل الزكاة، فلما أنزلت، جعلها الله طهرا للأموال.
Bukhari narrated it in the Book of Zakat (1404), saying, Ahmad bin Shabib bin Saeed said, our father narrated to us, from Yunus, from Ibn Shihab, from Khalid bin Aslam, who said, then he mentioned it. This appears on the surface to be a suspended (mualaq) chain, but according to the majority it is treated as connected, because Ahmad bin Shabib was among his own teachers.Ibn Majah also narrated it (1787) from Amr bin Sawad Misri, our father Abdullah bin Wahb narrated to us, from Ibn Lahia, from Aqeel, from Ibn Shihab, Khalid bin Aslam narrated to me, from Abdullah bin Umar, with the same wording, adding at the end that Ibn Umar said, "I would not mind having a mountain of gold, as long as I knew its number, paid zakat on it, and used it in obedience to Allah 
."This isnad is hasan because of the discussion surrounding Ibn Lahia, except that this particular narration comes through Abdullah bin Wahb, and the narrations of the Abadila (the group of companions named Abdullah) from him are more reliable than those of others.