Muwatta Malik, Book 49, Hadith 38 (USC-MSA)

Yahya related to me from Malik that Sadaqa ibn Yasar said, "I asked Said ibn al-Musayyab about wearing a ring. He said, 'Wear it, and tell people that I gave you that decision.' "

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ صَدَقَةَ بْنِ يَسَارٍ، أَنَّهُ قَالَ سَأَلْتُ سَعِيدَ بْنَ الْمُسَيَّبِ عَنْ لُبْسِ الْخَاتَمِ، فَقَالَ الْبَسْهُ وَأَخْبِرِ النَّاسَ، أَنِّي أَفْتَيْتُكَ بِذَلِكَ ‏.‏

sunnah.com

also referenced under: Book 49, Hadith 1712 (In-Book)