Narrated Al-Bara' bin 'Azib (RA):

The Prophet (ﷺ) sent 'Ali to Yemen. The narrator mentioned the complete Hadith. He said, "Ali sent a letter regarding their (the people of Yemen) acceptance of Islam. When Allah's Messenger (ﷺ) read the letter, he prostrated in gratitude to Allah the Most High for that." [Reported by al-Baihaqi].

وَعَنْ اَلْبَرَاءِ بْنِ عَازِبٍ ‏-رَضِيَ اَللَّهُ عَنْهُمَا‏- { أَنَّ اَلنَّبِيَّ ‏- صلى الله عليه وسلم ‏-بَعَثَ عَلِيًّا إِلَى اَلْيَمَنِ ‏- فَذَكَرَ اَلْحَدِيثَ ‏- قَالَ : فَكَتَبَ عَلِيٌّ ‏- رضى الله عنه ‏- بِإِسْلَامِهِمْ , فَلَمَّا قَرَأَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-اَلْكِتَابَ خَرَّ سَاجِدًا } رَوَاهُ اَلْبَيْهَقِيُّ .‏ [1]‏