‘Ā’ishah (may Allah be pleased with her) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) set out for Badr. When he reached Harrat al-Wabarah, a man met him who was known for his courage and support of others. The Companions of the Messenger of Allah (may Allah's peace and blessings be upon him) were pleased to see him. He said: "I have come so that I may follow you and get a share from the booty." The Messenger of Allah (may Allah's peace and blessings be upon him) said to him: "Do you believe in Allah and His Messenger?" He said: 'No.' The Messenger of Allah (may Allah's peace and blessings be upon him) said: "Then go back, for I will not seek help from a polytheist." He went on until we reached Ash-Shajarah, where the man met him again. The Prophet (may Allah's peace and blessings be upon him) asked him the same question again, and the man gave him the same answer. he said: "Then go back, for I will not seek help from a polytheist." The man returned and overtook him at Baydā'. He asked him as he had asked previously: "Do you believe in Allah and His Messenger?" The man said: 'Yes.' The Messenger of Allah (may Allah's peace and blessings be upon him) said to him: "Then come along with us."
شرح الحديث :
This Hadīth shows that when the Prophet (may Allah's peace and blessings be upon him) set forth to fight the disbelievers on the Day of Badr, a polytheist who was strong and courageous followed him to fight with him and get a share of the booty. The Prophet (may Allah's peace and blessings be upon him) asked him whether he believed in Allah and the Last Day, and the man told him that he did not. So the Prophet (may Allah's peace and blessings be upon him) stated that he would not seek the help of a polytheist, for polytheists are not to be trusted with protecting the believers. Treacherous as they could be, they might convey the news of Muslims to the disbelievers. However, the man came again to the Prophet (may Allah's peace and blessings be upon him) who then asked him whether he became a Muslim, and the answered in the affirmative. Hence, he asked him to join the army. The point of the Hadīth is that it is not permissible to seek the help of the polytheists in fighting, although it is permissible in the case of need and necessity, as indicated by other proofs.