Musannaf Ibn Abi Shayba 9:604

Abu Khalid al-Ahmar narrated to us, from Muhammad ibn Salim, from al-Sha’bi, from Shurayh, who said: Umar wrote to me that I should grant her (the wife of the missing person) a respite of one year. If he is able (to return), then (he should return), otherwise, I should give her a choice. If she wishes, she may remain, and if she wishes, she may separate from him.