Hadith: Ibn ‘Umar reported that ‘Umar ibn al-Khattāb wrote to the army commanders about men who stayed for a long time away from their wives. He ordered the [commanders] to charge them to either spend (on their wives) or divorce. If they divorce, they should send the financial support they had withheld

عن ابن عمر، أن عمر بن الخطاب -رضي الله عنه وعن ابنه-، كتب إلى أُمراء الأجْنادِ في رِجالٍ غابُوا عن نسائهم فأمرَهم أن يأخذوهم بأنْ يُنفقوا أو يُطلقوا، فإنْ طَلقوا بَعثوا بنفقة ما حَبَسُوا.
[صحيح] - [رواه الشافعي والبيهقي]

Ibn ‘Umar reported: ‘Umar ibn al-Khattāb wrote to the army commanders about the men who had stayed away from their wives (for a long time). He ordered the [commanders] to enjoin them to either spend (on their wives) or divorce. If they divorced, they should send the financial support they had withheld.
Sahih/Authentic. - [Al-Bayhaqi]

Explanation

This report shows that a husband is not allowed to stay away from his wife and leave her without any financial support. If he stays away without leaving any money for his wife, when he clearly does not have any resources, he is under an obligation to either send money to his wife or divorce her. If he divorces her, he should send maintenance to cover the period he had stayed away. Financial support of a wife is an obligation on a husband, which cannot be dropped due to the passage of time. If a wife agrees to give up her right to maintenance for the previous period, that is her choice.