How does one write to the People of the Book?

'Abdullah ibn 'Abbas related that Abu Sufyan ibn Harb sent him to Heraclius, the Byzantine Emperor, and he called for the letter of the Messenger of Allah which Dihya had brought to the governor of Busra, who in turn passed it on to Heraclius. He read it out, saying, 'In the name of Allah, the Merciful, the Compassionate, from Muhammad, the slave of Allah and His Messenger, to Heraclius, ruler of the Byzantines. Peace be upon the one who follows guidance. I call you to Islam. If you become Muslim, you will be safe and Allah will double your reward. If you turn away, then you incur the wrong action of your subjects. "O People of the Book! Come to a proposition which is the same for us and you (to His words) Bear witness that we are Muslims." (3:54)'"

حَدَّثَنَا أَبُو الْيَمَانِ، قَالَ: أَخْبَرَنَا شُعَيْبٌ، عَنِ الزُّهْرِيِّ قَالَ: أَخْبَرَنِي عُبَيْدُ اللهِ بْنُ عَبْدِ اللهِ بْنِ عُتْبَةَ، أَنَّ عَبْدَ اللهِ بْنَ عَبَّاسٍ أَخْبَرَهُ، أَنَّ أَبَا سُفْيَانَ بْنَ حَرْبٍ أَخْبَرَهُ: أَرْسَلَ إِلَيْهِ هِرَقْلُ مَلِكُ الرُّومِ، ثُمَّ دَعَا بِكِتَابِ رَسُولِ اللهِ ﷺ الَّذِي أُرْسِلَ بِهِ مَعَ دِحْيَةَ الْكَلْبِيِّ إِلَى عَظِيمِ بُصْرَى، فَدَفَعَهُ إِلَيَّ هِرَقْلُ فَقَرَأَهُ، فَإِذَا فِيهِ: بِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ، مِنْ مُحَمَّدٍ عَبْدِ اللهِ وَرَسُولِهِ إِلَى هِرَقْلَ عَظِيمِ الرُّومِ، سَلاَّمٌ عَلَى مَنِ اتَّبَعَ الْهُدَى، أَمَّا بَعْدُ، فَإِنِّي أَدْعُوكَ بِدِعَايَةِ الإِسْلاَمِ، أَسْلِمْ تَسْلَمْ، يُؤْتِكَ اللَّهُ أَجْرَكَ مَرَّتَيْنِ، فَإِنْ تَوَلَّيْتَ فَإِنَّ عَلَيْكَ إِثْمَ الأَرِيسِيِّينَ وَ {يَا أَهْلَ الْكِتَابِ تَعَالَوْا إِلَى كَلِمَةٍ سَوَاءٍ بَيْنَنَا وَبَيْنَكُمْ} إِلَى قَوْلِهِ: {اشْهَدُوا بِأَنَّا مُسْلِمُونَ}.