Pakiṇṇaka 22

The Buddha was staying at Vesālī. At that time, Bhaddā bhikkhunī put on a silk robe, and went to her relatives’ house. On the road, she was caught in a rainstorm. (The robe) became transparent like crystal, and her whole body was visible. A crowd of people walked around her and wanted to look at her. So she crouched down. The student depending on her stood at her side to shield her off. For this reason, the bhikkhunīs went and informed … She answered: “I really did this, World-honored One.” The Buddha said: “From now on, it’s no longer allowed for a bhikkhunī to wear silk robes. ‘Silk’ means the two kinds: raw silk and processed silk. ‘Raw’ means fine threads. ‘Processed’ means spun thread. If she wears fine-thread silk, she breaks a minor vinaya rule. If she wears spun-thread silk, she transgresses against vinaya and should mentally repent. If a bhikkhu wears it, there’s no offense.”