Al-Kāfi
Hadith 2017وَ بِهَذَا الْإِسْنَادِ قَالَ كَانَ عَلِيٌّ وَ الْحَسَنُ وَ الْحُسَيْنُ ( صلوات الله عليهم ) يَتَخَتَّمُونَ فِي أَيْسَارِهِمْ .
12. Through the same chain of narrators as that of the previous Hadith the following is narrated: “Abu ‘Abd Allah (a.s.), has said that Ali, al-Hassan and al-Husayn, ‘Alayhim al-Salam, would wear the ring on their left hands.’”