صَحِيحُ الْبُخَارِيِّ
Sahih al-Bukhari 2938
Fighting for the Cause of Allah (Jihaad)
The invitation to Islam is essential before declaring war
حَدَّثَنَا عَلِيُّ بْنُ الْجَعْدِ، أَخْبَرَنَا شُعْبَةُ، عَنْ قَتَادَةَ، قَالَ سَمِعْتُ أَنَسًا ـ رضى الله عنه ـ يَقُولُ لَمَّا أَرَادَ النَّبِيُّ صلى الله عليه وسلم أَنْ يَكْتُبَ إِلَى الرُّومِ، قِيلَ لَهُ إِنَّهُمْ لاَ يَقْرَءُونَ كِتَابًا إِلاَّ أَنْ يَكُونَ مَخْتُومًا. فَاتَّخَذَ خَاتَمًا مِنْ فِضَّةٍ، فَكَأَنِّي أَنْظُرُ إِلَى بَيَاضِهِ فِي يَدِهِ، وَنَقَشَ فِيهِ مُحَمَّدٌ رَسُولُ اللَّهِ.
Narrated Anas: When the Prophet (ﷺ) intended to write a letter to the ruler of the Byzantines, he was told that those people did not read any letter unless it was stamped with a seal. So, the Prophet (ﷺ) got a silver ring-- as if I were just looking at its white glitter on his hand ---- and stamped on it the expression "Muhammad, Messenger of Allah".
Sahih al-Bukhari, 2938Sahihصحيح