Abu Musa sought permission to enter upon Umar three times, but he was not granted permission, so he left. Umar then sent for him and asked, "What made you turn back?"Abu Musa replied, "I sought permission in the manner the Messenger of Allah ﷺ instructed us, three times. If we are granted permission, we enter, and if not, we return."Umar said, "You must bring me proof of this, or I will deal with you."So Abu Musa went to the gathering of his people and implored them, and they testified on his behalf, so Umar let him go.
حدثنا أبو بكر حدثنا يزيد بن هارون أنبأنا داود بن أبي هند عن أبي نضرة
أن أبا موسى استأذن على عمر ثلاثا فلم يؤذن له فانصرف فأرسل إليه عمر ما ردك قال استأذنت الاستئذان الذي أمرنا به رسول الله ﷺ ثلاثا فإن أذن لنا دخلنا وإن لم يؤذن لنا رجعنا قال فقال لتأتيني على هذا ببينة أو لأفعلن فأتى مجلس قومه فناشدهم فشهدوا له فخلى سبيله
[Sahih] Ahmad narrated it: 4/410,418, 3/19 from Yazid through this route, and Muslim narrated it, in the Book of Manners, Chapter on Seeking Permission, no. 2153/35, from the hadith of Abu Nadra through this route. It also has another route in Bukhari, no. 6245, and Muslim, no. 2153/34, and others besides them.