Shiva Purana
आयसौ स्रुक्स्रुवौ कार्यौ मारणादिषु कर्मसु ॥ तदन्यत्र तु सौवर्णौ शांतिकाद्येषु कृत्स्नशः ॥ ४३ ॥
In Māraṇa and other rites the Śruk and Śruva shall be made of iron. In all other rites such as quiescent these shall be made of gold.
english translation
Ayasau sruksruvau kAryau mAraNAdiSu karmasu ॥ tadanyatra tu sauvarNau zAMtikAdyeSu kRtsnazaH ॥ 43 ॥
hk transliteration by Sanscript