What is the grade of the hadith about repentance of the man who killed 100 people?

> Abu Sa'id Al-Khudri (May Allah be pleased with him) reported: > > Prophet of Allah (ﷺ) said: "There was a man from among a nation before > you who killed ninety-nine people and then made an inquiry about the > most learned person on the earth. He was directed to a monk. He came > to him and told him that he had killed ninety-nine people and asked > him if there was any chance for his repentance to be accepted. He > replied in the negative and the man killed him also completing one > hundred. > > He then asked about the most learned man in the earth. He was directed > to a scholar. He told him that he had killed one hundred people and > asked him if there was any chance for his repentance to be accepted. > He replied in the affirmative and asked, 'Who stands between you and > repentance? Go to such and such land; there (you will find) people > devoted to prayer and worship of Allah, join them in worship, and do > not come back to your land because it is an evil place.' > > So he went away and hardly had he covered half the distance when death > overtook him; and there was a dispute between the angels of mercy and > the angels of torment. The angels of mercy pleaded, 'This man has come > with a repenting heart to Allah,' and the angels of punishment argued, > 'He never did a virtuous deed in his life.' Then there appeared > another angel in the form of a human being and the contending angels > agreed to make him arbiter between them. > > He said, 'Measure the distance between the two lands. He will be > considered belonging to the land to which he is nearer.' They measured > and found him closer to the land (land of piety) where he intended to > go, and so the angels of mercy collected his soul". > > [Al-Bukhari and Muslim]. > > In another version: "He was found to be nearer to the locality of the > pious by a cubit and was thus included among them". Another version > says: "Allah commanded (the land which he wanted to leave) to move > away and commanded the other land (his destination) to draw nearer and > then He said: "Now measure the distance between them.' It was found > that he was nearer to his goal by a hand's span and was thus > forgiven". It is also narrated that he drew closer by a slight > movement on his chest. > > Arabic/English book reference : Book 1, Hadith 20 I quoted it from Sunnah.com » Riyad as-Salihin » The Book of Miscellany. It says [Al-Bukhari and Muslim] but doesn't provide any information regarding its grade. I searched Google but couldn't find it on Bukhari or Muslim. My questions are, - What is it's grade? - Is it a sahih hadith? - Is it reported in Bukhari and Muslim?