Tirmidhī's al-Jāmiʿ al-Ṣaḥīḥ is considered to be one of the most important books in the Kutub al-Sittah. He asked questions about the hadiths and their ilal (the unclear, hidden problematic defects of the narration) that includes in his book to important muhaddith of his period such as Abū Zur'a al-Rāzī (d. 264/878), al-Bukhārī (d. 256/870), and al-Dārimī (d. 255/869) and mentioned these questions in his book. After complied his book, Tirmidhī sent it to many different regions and gained the appreciation of famous scholars there. He pointed to the reliability of his work when he said, "Whoever has this book in his house means there is a Prophet speaking in his house." Tirmidhī is a scholar who has distinguished very well the defects that harm the authenticity of hadith and are difficult to detect, and who has made important contributions to the science of ilal. With his works in the field of ilal, he showed that he was a strong critic of hadith. In his most important work, al-Jāmiʿu ṣ-Ṣaḥīḥ, he demonstrated his deep knowledge in this field by making preferences between narrations. This study aims to contribute to revealing this aspect of Tirmidhī. Every author writes his book for a purpose. He reveals this purpose through the methods that he follows. In this sense, revealing the methods followed by an author in writing his book means revealing his purpose. Tirmidhī composited his book according to the fiqh chapters and first mentioned the hadith that was in dispute or hadith with a problem and then mentioned the saheeh narration. Islamic scholars who have studied the methods of hadith books have mentioned many different methods that Tirmidhī used in his book. Repetition of hadiths, his specialization in the text and sanad, including jarh and ta'dīl information about the narrators, stating the degree of authenticity of the hadith, and touching upon the opinions of different sects and scholars about the hadith are some of these methods. This study examines Tirmidhī's methodology regarding the criteria according to which he prefers hadiths with a special focus on the chapter of Siyar. The primary sources were the commentaries on al-Jāmiʿu al-Ṣaḥīḥ and the books of ilal, cerh, and taʿdīl. Among these commentaries are ʿAriżat al-Aḥwadhī fī sharḥ al-Tirmidhī by Abū Bakr Ibn al-ʿArabī (d. 543/1148), al-Kashmirī's (d. 1933), al-Arfu al-Shazi Sharh al-Ṣaḥīḥ al-Tirmidhī, and al-Mubārakfūrī's (d. 1934) Tuḥfat al-aḥwazī bi-sharḥi Jāmiʿi al-Tirmidhī. As for the Ilāl type of sources, the first one is al-Tirmidhī's (d. 279/892) al-ʿIlāl al-Ṣaġīr, followed by Ahmad b. Ḥanbal's (d. 241/855) Kitāb al-ʿIlāl wa maʿrifat al-ricāl. On the subject of Jarh and Ta'dīl, Ibn Abū Hātim al-Rāzī's (d. 327/938) al-Jarh wa't-Ta'dīl was consulted. Seventy hadiths were mentioned in the chapter of siyar, which we will discuss. These hadiths were analyzed one by one to determine the reasons for Tirmidhī's preference among the hadiths, and it was seen that he made a preference for 8 hadiths in the Siyar section. As an example of these, he has mentioned the unclear, hidden problematic defects of al-Bahṭarī's narration from Salmān al-Fārisī due to the incompleteness of the narration and preferred the other complete narrations. Another example is that he accepted the narration about the distribution of the spoils through 'Abdullah b. 'Umar because its narrators were thika', and he did not prefer the narration of Mujammi' b. Jariyah, Ibn 'Abbas, and Abu 'Amrah because they were weak and unknown narrators. As a result, we can say that when he prefers hadiths, he takes into account whether they are muttaasıl, munkati', marfū, mawquf, Ṣaḥīḥ or weak, or whether they can be acted upon in terms of fiqh.