If an infidel warrior comes in an Islamic territory

Narrated Salama bin Al-Akwa:

"An infidel spy came to the Prophet while he was on a journey. The spy sat with the companions of the Prophet and started talking and then went away. The Prophet ﷺ said (to his companions), 'Chase and kill him.' So, I killed him." The Prophet then gave him the belongings of the killed spy (in addition to his share of the war booty).

حَدَّثَنَا أَبُو نُعَيْمٍ، حَدَّثَنَا أَبُو الْعُمَيْسِ، عَنْ إِيَاسِ بْنِ سَلَمَةَ بْنِ الأَكْوَعِ، عَنْ أَبِيهِ، قَالَ أَتَى النَّبِيَّ ﷺ عَيْنٌ مِنَ الْمُشْرِكِينَ وَهْوَ فِي سَفَرٍ، فَجَلَسَ عِنْدَ أَصْحَابِهِ يَتَحَدَّثُ ثُمَّ انْفَتَلَ، فَقَالَ النَّبِيُّ ﷺ " اطْلُبُوهُ وَاقْتُلُوهُ ". فَقَتَلَهُ فَنَفَّلَهُ سَلَبَهُ.