That the Messenger of Allah ﷺ advanced towards Badr till he reached Harrah Al-Wabr where he was met by a man from the idolaters, about whom it was said he was brave and courageous. The Prophet ﷺ said to him: "Do you believe in Allah and his Messenger?" He said: "No." He said: "Then return, because we do not seek aid from an idolater." The Hadith has more dialogue than this. And this is a Hasan Gharib Hadith. This is acted upon according to some of the people of knowledge. They say that the people of Adh-Dhimmah do not recieve a share, even it they were to fight along with the Muslims against the enemy. Some of the people of knowledge said that they are given a share when they attend the battle with the Muslims.  

أَنَّ رَسُولَ اللَّهِ ﷺ خَرَجَ إِلَى بَدْرٍ حَتَّى إِذَا كَانَ بِحَرَّةِ الْوَبَرِ لَحِقَهُ رَجُلٌ مِنَ الْمُشْرِكِينَ يَذْكُرُ مِنْهُ جُرْأَةً وَنَجْدَةً فَقَالَ لَهُ النَّبِيُّ ﷺ أَلَسْتَ تُؤْمِنُ بِاللَّهِ وَرَسُولِهِ قَالَ لاَ قَالَ ارْجِعْ فَلَنْ أَسْتَعِينَ بِمُشْرِكٍ وَفِي الْحَدِيثِ كَلاَمٌ أَكْثَرُ مِنْ هَذَا هَذَا حَدِيثٌ حَسَنٌ غَرِيبٌ وَالْعَمَلُ عَلَى هَذَا عِنْدَ بَعْضِ أَهْلِ الْعِلْمِ قَالُوا لاَ يُسْهَمُ لأَهْلِ الذِّمَّةِ وَإِنْ قَاتَلُوا مَعَ الْمُسْلِمِينَ الْعَدُوَّ وَرَأَى بَعْضُ أَهْلِ الْعِلْمِ أَنْ يُسْهَمَ لَهُمْ إِذَا شَهِدُوا الْقِتَالَ مَعَ الْمُسْلِمِينَ