Abu Saeed Khudri reported,

The Prophet of Allah ﷺ said, "Among the people before you was a man who had killed ninety-nine souls. He asked about the most knowledgeable person on earth, and he was directed to a monk. He went to him and said that he had killed ninety-nine souls and asked whether he could repent. The monk said, 'No.' So he killed him, completing one hundred.Then he asked again about the most knowledgeable person on earth, and he was directed to a learned man. He told him that he had killed a hundred souls and asked whether he could repent. The man replied, 'Yes, and who could stand between you and repentance? Go to such-and-such a land, for there are people there who worship Allah. Worship Allah with them, and do not return to your own land, for it is an evil land.'So he set off, but when he had reached the midpoint of the journey, death came to him. The angels of mercy and the angels of punishment disputed over him. The angels of mercy said, 'He came as one repenting, turning his heart toward Allah.' The angels of punishment said, 'He never did any good at all.'Then an angel came to them in the form of a human being, and they made him their judge. He said, 'Measure the distance between the two lands. Whichever is nearer, he belongs to it.' They measured and found that he was nearer to the land he had been heading toward, so the angels of mercy took him."Qatada said that al-Hasan said, "It was mentioned to us that when death came to him, he strained forward with his chest."

Muslim 7008

Sahih

حدثنا محمد بن المثنى ومحمد بن بشار واللفظ لابن المثنى قالا حدثنا معاذ بن هشام حدثني أبي عن قتادة عن أبي الصديق

عن أبي سعيد الخدري

أن نبي الله ﷺ قال كان فيمن كان قبلكم رجل قتل تسعة وتسعين نفسا فسأل عن أعلم أهل الأرض فدل على راهب فأتاه فقال إنه قتل تسعة وتسعين نفسا فهل له من توبة فقال لا فقتله فكمل به مائة ثم سأل عن أعلم أهل الأرض فدل على رجل عالم فقال إنه قتل مائة نفس فهل له من توبة فقال نعم ومن يحول بينه وبين التوبة انطلق إلى أرض كذا وكذا فإن بها أناسا يعبدون الله فاعبد الله معهم ولا ترجع إلى أرضك فإنها أرض سوء فانطلق حتى إذا نصف الطريق أتاه الموت فاختصمت فيه ملائكة الرحمة وملائكة العذاب فقالت ملائكة الرحمة جاء تائبا مقبلا بقلبه إلى الله وقالت ملائكة العذاب إنه لم يعمل خيرا قط فأتاهم ملك في صورة آدمي فجعلوه بينهم فقال قيسوا ما بين الأرضين فإلى أيتهما كان أدنى فهو له فقاسوه فوجدوه أدنى إلى الأرض التي أراد فقبضته ملائكة الرحمة قال قتادة فقال الحسن ذكر لنا أنه لما أتاه الموت نأى بصدره

مسلم 7008صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Muslim
Book
Tawba
Chapter
Acceptance of the repentance of a killer even if his killing was frequent
Numbering
Darussalam 7008
Muslim 7008