Alqamah (may Allah have mercy on him) said that the wife of Abdullah (may Allah be pleased with him) asked about jewelry, and he said: When it reaches two hundred dirhams, zakah is due on it. She said: I will spend that zakah on my nephews who are under my care. He said: Very well.
This has also been narrated as marfu' (attributed to the Prophet (peace and blessings be upon him)), but that is of no weight.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7546