I heard the Messenger of Allah ﷺ say, "The guarantor is liable, and the debt must be repaid."
سمعت رسول الله ﷺ يقول: الزعيم غارم، والدين مقضي.
Abu Dawud (3565), Tirmidhi (1265), Ibn Majah (2405), Bayhaqi (726), and Ahmad (22294) all narrated it, all of them through the hadith of Ismail bin Ayyash, who said, Shurahbil bin Muslim Khawlani told me, he said, I heard Abu Umama say, and then he related it.This is a long hadith, and its parts have been mentioned scattered throughout the books of the sunnah. The complete version, as mentioned by Ahmad and others, is that the Prophet ﷺ delivered a sermon in the year of the Farewell Pilgrimage and said, "Allah has given every person with a right their due, so there is no bequest for an heir, the child belongs to the marriage bed, and for the fornicator is the stone, and their reckoning is with Allah. Whoever claims descent from someone other than his father, or claims allegiance to someone other than his masters, upon him is the curse of Allah, following him until the Day of Resurrection. A woman may not spend anything from her household except with her husband's permission." It was said, "O Messenger of Allah, not even food?" He said, "That is the best of our wealth." Then he said, "A loan must be returned, a gift must be given back if withheld, a debt must be paid, and the guarantor is liable."Tirmidhi said, hasan gharib. I say, it is as he said, for Ismail bin Ayyash is hasan in his narration from the people of his own region, the Syrians, and this narration belongs to that category. It is only narrated through his route. Shurahbil bin Muslim is a subject of disagreement among scholars, but his hadith is hasan. Some of its statements have supporting narrations from other companions, which have been documented in their respective places.