Abu Wa’il told that Khalid b. al-Walid wrote to the people of Persia: In the name of God, the Compassionate, the Merciful. From Khalid b. al-Walid to Rustum and Mih'an among the nobles of Persia. Peace be to those who follow the guidance. To proceed: We summon you to Islam, but if you refuse then pay the jizya in subjection feeling humbled (Cf. Al-Qur'an, 9:29). If you refuse to do that, I have with me people who love being killed in God’s path as the Persians love wine. Peace be to those who follow the guidance. It is transmitted in Sharh as-sunna.
Source: sunnah.com
Other translations
Arabic
عَن أبي وائلٍ قَالَ: كَتَبَ خَالِدُ بْنُ الْوَلِيدِ إِلَى أَهْلِ فَارِسَ: بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ مِنْ خَالِدِ بْنِ الْوَلِيدِ إِلَى رُسْتَمَ وَمِهْرَانَ فِي مَلَأِ فَارِسَ. سَلَامٌ عَلَى مَنِ اتَّبَعَ الْهُدَى. أَمَّا بَعْدُ فَإِنَّا نَدْعُوكُمْ إِلَى الْإِسْلَامِ فَإِنْ أَبَيْتُمْ فَأَعْطُوا الْجِزْيَةَ عَنْ يَدٍ وَأَنْتُمْ صَاغِرُونَ فَإِنْ أَبَيْتُمْ فَإِنَّ مَعِيَ قَوْمًا يُحِبُّونَ الْقَتْلَ فِي سَبِيلِ اللَّهِ كَمَا يُحِبُّ فَارِسُ الْخَمْرَ وَالسَّلَامُ عَلَى مَنِ اتَّبَعَ الْهُدَى. رَوَاهُ فِي شَرْحِ السّنة 0
sunnah.com