Al-Adab Al-Mufrad, Book 27, Hadith 478 (In-Book) ⓘ

Hanash ibn al-Harith reported that his father said, "One of our men had a mare which became pregnant which he then slaughtered, saying, 'Will I live long enough to ride this horse?' Then we received 'Umar's letter telling us to attend to the provision that Allah has given us in order to make it thrive since there is still time in the business."

حَدَّثَنَا أَبُو نُعَيْمٍ، قَالَ‏:‏ حَدَّثَنَا حَنَشُ بْنُ الْحَارِثِ، عَنْ أَبِيهِ قَالَ‏:‏ كَانَ الرَّجُلُ مِنَّا تُنْتَجُ فَرَسُهُ فَيَنْحَرُهَا فَيَقُولُ‏:‏ أَنَا أَعِيشُ حَتَّى أَرْكَبَ هَذَا‏؟‏ فَجَاءَنَا كِتَابُ عُمَرَ‏:‏ أَنْ أَصْلِحُوا مَا رَزَقَكُمُ اللَّهُ، فَإِنَّ فِي الامْرِ تَنَفُّسًا‏.‏