It is narrated from Ibn Shubrumah (may Allah have mercy on him) that Umar bin Abd al-Aziz (may Allah have mercy on him) wrote concerning the wife of the missing husband that she should wait and be patient.
A musnad hadith has also been narrated on this, but its chain contains someone whose hadith is not used as evidence.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15564