Ibn Taymiyya wrote to a Christian king in Cyprus who was holding Muslim prisoners. He reminded him that he asked the Mongol leaders to free the Christian prisoners. And they were all set free.
1. Ibn Taymiyah said to the king in his letter:
ثم عند المسلمين من الرجال الفداوية الذين يغتالون الملوك في فرشها وعلى أفراسها.
Then, among the Muslims, there are men willing to sacrifice themselves, who kill kings on their thrones and while riding their horses.
الرسالة القبرصية by Ibn Taymiyyah
2. He also mentioned that Muslims always do good to Christian captives and we want same in return, he also spoke against trinity and asked him to accept Islam.
3. Ibn Kathir said:
وفي هذا اليوم خرج الشيخ تقي الدين بن تيمية إلى مخيم بولاي فاجتمع به في فكاك من كان معه من أسارى المسلمين، فاستنقذ كثيرا منهم من أيديهم،
That day Shaykh Ibn Taymiyyah went to the camp of Bolaai (who killed many Muslims), and he spoke to him regarding Muslim captives which were in his custody. Then He (Ibn Taymiyyah) made him free many of the captives (which includes muslim, jews and christians). [Al Bidaya wal Nihaya vol 14 page 24]
4. He asked them to free the Christians and Jews.
Ibn Taymiyyah said:
وقد عرف النصارى كلهم إني لما خاطبت التاتار في إطلاق الأسرى وأطلقهم غازان وقطلوشاه، وخاطبت مولاي فيهم، فسمح بإطلاق المسلمين قال لي: لكن معنا نصارى أخذناهم من القدس فهؤلاء لا يطلقون، فقلت له: بل جميع من معك من اليهود والنصارى الذين هم أهل ذمتنا فإنا نفتكّهم، ولا ندع أسيرا لا من أهل الملة ولا من أهل الذمة، وأطلقنا من النصارى من شاء الله فهذا عملنا وإحساننا والجزاء على الله.
All the Christians know that when I appealed to the mongols to release the prisoners, Ghazan and Qatlushah released them. And I appealed to Molay regarding them, so he permitted the release of the Muslims. He said to me: ‘But we have Christians who were taken from Jerusalem, and these will not be released.’ So I said to him: ‘Rather, you will release all the Jews and Christians who are under Muslim protection. We will not leave any prisoner, whether Muslim or from ahlul dhimma. And they released Christians by the will of Allah. This is our deed and kindness, and the reward is from Allah.'”
[al-Risalah al Qabrasiyah by Shaykh Ibn Taymiyyah page no. 22]