(44) The Book of Financial Transactions
كتاب البيوع
(102) Chapter: Taking On Another's Debt
(102) باب الْكَفَالَةِ بِالدَّيْنِ
Sunan an-Nasa'i 4692 
It was narrated from 'Abdullah bin Abi Qatadah, from his father, that a man from among the Ansar was brought to the prophet for him to offer the funeral prayer, and he said:
"Your companion owes a debt. " Abu Qutdah said: "I will guarantee it for him. "The prophet said: "In full?" He said: "In full." (Sahah)
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا خَالِدٌ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ عُثْمَانَ بْنِ عَبْدِ اللَّهِ بْنِ مَوْهَبٍ، عَنْ عَبْدِ اللَّهِ بْنِ أَبِي قَتَادَةَ، عَنْ أَبِيهِ، أَنَّ رَجُلاً، مِنَ الأَنْصَارِ أُتِيَ بِهِ النَّبِيُّ صلى الله عليه وسلم لِيُصَلِّيَ عَلَيْهِ فَقَالَ ‏"‏ إِنَّ عَلَى صَاحِبِكُمْ دَيْنًا ‏"‏ ‏.‏ فَقَالَ أَبُو قَتَادَةَ أَنَا أَتَكَفَّلُ بِهِ ‏.‏ قَالَ ‏"‏ بِالْوَفَاءِ ‏"‏ ‏.‏ قَالَ بِالْوَفَاءِ ‏.‏
Reference : Sunan an-Nasa'i 4692
In-book reference : Book 44, Hadith 244
English translation : Vol. 5, Book 44, Hadith 4696