Hadith.4727 - It was narrated from Harun ibn Muslim who said
I wrote to the 'Sahib al-Dar' (Master of the House Imam Muhammad ibn Hassan Al-Mahdi (as)) saying: "A child was born to me, and I shaved his head, weighed his hair in dirhams, and gave its equivalent in charity."
Imam (as) replied: "It is not permissible to weigh it except with gold or silver, and this is the established Sunnah."