Musannaf Ibn Abi Shayba 9:814

'Abd al-A'la narrated to us, from Ma'mar, from al-Zuhri, from Sa'id ibn al-Musayyib, that 'Umar ibn al-Khattab and 'Uthman ibn 'Affan said regarding the wife of a missing person: She shall wait for four years, and she shall observe an 'iddah (waiting period) of four months and ten days.