بُلُوغُ الْمَرَامِ
Bulugh al-Maram 1148
Marriage
وَعَنْ عُمَرَ - رضى الله عنه - { أَنَّهُ كَتَبَ إِلَى أُمَرَاءِ اَلْأَجْنَادِ فِي رِجَالٍ غَابُوا عَنْ نِسَائِهِمْ: أَنْ يَأْخُذُوهُمْ بِأَنَّ يُنْفِقُوا أَوْ يُطَلِّقُوا, فَإِنْ طَلَّقُوا بَعَثُوا بِنَفَقَةِ مَا حَبَسُوا } . أَخْرَجَهُ اَلشَّافِعِيُّ. ثُمَّ اَلْبَيْهَقِيّ بِإِسْنَادِ حَسَنٌ [1] .
Narrated 'Umar: He wrote (letters) to the commanders of the armies regarding some men (soldiers) who have been absent from their wives, that they should impose upon them to spend on their wives or divorce them; and if they divorce them they should then send the maintenance which they have withheld. [ash-Shafi'i reported it, then al-Baihaqi with a Hasan (good) chain of narrators].
Sunnah.com reference: Book 8, Hadith 213