NASAI-KUBRA 8794:
from ʿAbdullāh b. ʿAbbās —
[Machine] He informed him that the Messenger of Allah wrote to Caesar, inviting him to Islam, and sent his letter with Dihyah al-Kalbi. The Messenger of Allah commanded him to deliver it to 'Azim Busr to deliver it to Caesar. 'Azim Busr delivered it to Caesar. When Allah revealed his victory over the Persian army, Caesar walked from Hims to Iliya in gratitude to Allah. When the letter of the Messenger of Allah reached Caesar, he said when he read it, "Is there anyone from his people here who can ask him about the Messenger of Allah?"
الكبرى للنسائي ٨٧٩٤:
عن عبد الله بن عباس —
أَخْبَرَهُ أَنَّ رَسُولَ اللهِ ﷺ كَتَبَ إِلَى قَيْصَرَ يَدْعُوهُ إِلَى الْإِسْلَامِ وَبَعَثَ بِكِتَابِهِ مَعَ دِحْيَةَ الْكَلْبِيِّ وَأَمَرَهُ رَسُولُ اللهِ ﷺ أَنْ يَدْفَعَهُ إِلَى عَظِيمِ بُصْرَى لِيَدْفَعَهُ إِلَى قَيْصَرَ فَدَفَعَهُ عَظِيمُ بُصْرَى إِلَى قَيْصَرَ وَكَانَ قَيْصَرُ لَمَّا كَشَفَ اللهُ عَنْهُ جُنُودَ فَارِسَ مَشَى مِنْ حِمْصَ إِلَى إِيلِيَاءَ شُكْرًا لَمَّا أَبْلَاهُ اللهُ فَلَمَّا جَاءَ قَيْصَرَ كِتَابُ رَسُولِ اللهِ ﷺ قَالَ حِينَ قَرَأَهُ «الْتَمِسُوا هَلْ هَاهُنَا مِنْ قَوْمِهِ مِنْ أَحَدٍ لِيَسْأَلَهُ عَنْ رَسُولِ اللهِ ﷺ؟ » مُخْتَصَرٌ
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