Abdullah bin Abu Awfa wrote to Umar bin Ubaydullah when he marched against the Haruriyya, informing him that the Messenger of Allah ﷺ, on one of the days when he met the enemy, would wait until the sun had passed its zenith, then he would stand among the people and say, "People, do not wish to meet the enemy. Ask Allah for safety. But when you do meet them, be steadfast, and know that Paradise lies beneath the shade of the swords."Then the Prophet ﷺ stood and said, "O Allah, Revealer of the Book, Mover of the clouds, Defeater of the confederates, defeat them and grant us victory over them."
و حدثني محمد بن رافع حدثنا عبد الرزاق أخبرنا ابن جريج أخبرني موسى بن عقبة عن أبي النضر
له عبد الله بن أبي أوفى فكتب إلى عمر بن عبيد الله حين سار إلى الحرورية يخبره أن رسول الله ﷺ كان في بعض أيامه التي لقي فيها العدو ينتظر حتى إذا مالت الشمس قام فيهم فقال يا أيها الناس لا تتمنوا لقاء العدو واسألوا الله العافية فإذا لقيتموهم فاصبروا واعلموا أن الجنة تحت ظلال السيوف ثم قام النبي ﷺ وقال اللهم منزل الكتاب ومجري السحاب وهازم الأحزاب اهزمهم وانصرنا عليهم
Both of them (Bukhari and Muslim) reported together the hadith of Musa bin Uqba, from Abu Nadr, the freed slave of Umar, who said, Ibn Abu Awfa wrote to him, and I read it, that the Prophet, peace and blessings be upon him and his family, said, "Do not wish to encounter the enemy, and when you do meet them, be patient, and know that Paradise lies beneath the shade of swords."This is sahih and serves as evidence for the permissibility of ijaza and written transmission, since Abu Nadr did not hear this directly from Ibn Abu Awfa but only saw it in his letter. And success comes from Allah.
Ibn Hajar, may Allah have mercy on him, said in the introduction to Fath al-Bari, page 361, after mentioning Daraqutni's statement,"I say, there is no defect in it, but this depends on whether the condition for transmission by written correspondence is that it be specifically from the writer to the one to whom he wrote, or whether anyone who recognizes the handwriting may narrate by it, even if he was not the person the letter was addressed to. The first is what is immediately understood from the term, while the second is, according to them, one of the forms of transmission by discovering a written text.However, it could be said here that Abu Nadr's narration in this case is from his patron Umar bin Ubaydullah, from the letter that Ibn Abu Awfa wrote to him, and that he took this from his patron by recitation, because he read it aloud to him, since he was his scribe. In that case, it would become a transmission by written correspondence, as Daraqutni said. And Allah knows best."This is what Ibn Hajar, may Allah have mercy on him, said. And in Fath al-Bari, volume 5, page 156, he said that this is the apparent view.
I say, what appears to me is that the narration of Abu Nadr is not from his master, but rather from the letter of Abdullah bin Abu Awfa, as found in Sahih Muslim, volume 12, page 46. It contains, from Abu Nadr, from the letter of a man from Aslam among the companions of the Prophet, peace and blessings be upon him and his family, called Abdullah bin Abu Awfa, who wrote to Umar bin Ubaydullah when he set out against the Kharijites, informing him that the Messenger of Allah, peace and blessings be upon him and his family, and then he mentioned it. Had it been as it appeared to the Hafiz, then the mention of Umar bin Ubaydullah would place him among the men of the two Shaykhs, yet he is not found in Tahdhib al-Tahdhib. And Allah knows best.