Hasan and Husayn used to wear their rings on their left hands. This is a hasan sahih hadith.
حدثنا قتيبة حدثنا حاتم بن إسمعيل
كان الحسن والحسين يتختمان في يسارهما هذا حديث حسن صحيح
Its chain is daif. Tabarani transmitted it in Kabir 23/3, no. 2540, from the hadith of Hatim, and Bayhaqi 4/143 from the hadith of Jafar, both at length and in abridged form, but the chain is disconnected.