Praise be to Allah.
the question is Has Allah Forgiven Those Who Participated in the Battle of Badr? Those who fought and participated in the battle of Badr. And specifically, those who fought in the support of Islam were been rewarded by Allah (may He be glorified).
Al-Bukhari related from Humayd that he heard Anas say: Harithah was killed in the Battle of Badr, so his mother came to the Messenger of Allah, peace and blessings of Allah be upon him, and said: “O Allah’s Messenger! Inform me about Harithah. If he is in Paradise, I shall remain patient, but if it is not so, then you shall see what I do (i.e. of wailing)?”
Allah’s Messenger said to her: “Woe to you! Have you lost your senses? Do you think Paradise is only one (level)? It has many wonderful gardens and your son is in the (most superior) garden of Paradise, Al-Firdaus.”
Al-Bukhari and Muslims both related from ‘Ali Ibn Abi Talib the story of Hatib Ibn Abi Balta’ah and his sending of a letter to the people of Makkah in the year of the conquest. ‘Umar sought the permission of the Messenger of Allah to behead him for he had betrayed Allah, His Messenger and the Believers.
In response, the Messenger of Allah, peace and blessings of Allah be upon him, said: “He participated in the Battle of Badr and who knows, perhaps Allah has already looked at the Badr warriors and said, ‘Do whatever you like, for I have forgiven you.” ‘Umar’s eyes welled with tears and he said: “Allah and His Messenger know best.”
Imam Muslims related that Jabir narrated that a slave of Hatib came to the Messenger of Allah, peace be upon him, complaining against him, then he said: “O Messenger of Allah, Hatib will definitely enter the Fire.” Whereupon the Messenger of Allah, peace and blessings of Allah be upon him, said: “You have lied, he will never enter it for he participated in the Battle of Badr and Al-Hudaibiyyah.”
Imam Ahmad related from Abu Hurairah that the Prophet said: “Allah looked at the warriors of Badr and said, ‘Do whatever you like, for I have forgiven you.” Abu Dawood has also related it from Ahmad Ibn Sinan and Moosa Ibn Ismael, both of whom related it from Yazeed Ibn Haaroon. Al-Bukhari related that Mu‘adh Ibn Rifa‘ah Ibn Rafi‘ Az-Zuraqi narrated that his father, who was one of those who witnessed the Battle of Badr, said: “Jibraeel came to the Messenger of Allah, peace and blessings of
Allah be upon him, and said, “How do you look upon the warriors of Badr among yourselves?” The Messenger of Allah, peace and blessings of Allah be upon him, said, “As the best of the Muslims,” or said a similar statement. On that, Jibraeel said, “And so are the angels who participated in Badr.” Al-Bukhari reported it exclusively.
In short, with all the hadith listed above. It’s clear that Allah (may He be glorified) has forgiven those who participate in the Battle if Badr.
And He knows best.