An army of the Ansar was stationed in the land of Persia with their commander. Umar used to rotate the armies every year, but he became preoccupied and overlooked them. When their term had passed, the people of that frontier post returned home. Umar dealt with them harshly and rebuked them, though they were companions of the Messenger of Allah ﷺ.They said, "Umar, you neglected us and abandoned in our case what the Messenger of Allah ﷺ commanded, that one group of fighters be relieved by another."
حدثنا موسى بن إسمعيل حدثنا إبراهيم يعني ابن سعد حدثنا ابن شهاب
أن جيشا من الأنصار كانوا بأرض فارس مع أميرهم وكان عمر يعقب الجيوش في كل عام فشغل عنهم عمر فلما مر الأجل قفل أهل ذلك الثغر فاشتد عليهم وتواعدهم وهم أصحاب رسول الله ﷺ فقالوا يا عمر إنك غفلت عنا وتركت فينا الذي أمر به رسول الله ﷺ من إعقاب بعض الغزية بعضا
[Its chain is hasan] Bayhaqi narrated it, 9/29, from the hadith of Abu Dawud through this route, and Ibn Jarud graded it sahih, hadith no. 1095.Ibn Shihab Zuhri explicitly stated that he heard it directly, and Abdullah bin Kaab heard it from the companions and from Umar, as appears to be the case.