It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that he said: "The one who wrote the document (of the treaty) on the day of the Treaty of al-Hudaybiyah was Sayyiduna Ali bin Abi Talib (may Allah be pleased with him)."
This chain is sahih (authentic), and it has a supporting report (shahid) in the Sahih (al-Bukhari and Muslim) from the hadith of Sayyiduna al-Miswar (may Allah be pleased with him) and others.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب السيرة والمغازي / 4286
Hadith Gradingمحدثین:إسناده صحيح
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :قال ابن حجر: هَذَا إِسْنَادٌ صَحِيحٌ ، لَهُ شَاهِدٌ فِي الصَّحِيحِ مِنْ حَدِيثِ الْمِسْوَرِ رَضِيَ اللهُ عَنْهُ وَغَيْرِهِ . » «أخرجه مصنف عبد الرزاق برقم: 9721»