Couldn't find it in Bukhari, but it's mentioned in all 4 Sunan collections.
Abu Dawud Book 35 Hadith Number 4579, Tirmidhi Book 43 Hadith Number 2649, Ibn Majah Book 36 Hadith Number 3991:
Narated By Abu Hurairah : The Prophet said: "The Jews were split up into seventy one or seventy two sects; and the Christians were split up into seventy one or seventy two sects; and my community will be split up into seventy three sects."
Tirmidhi Book 43, Hadith Number 2650:
Abdullah ibn Amr reported that Allah’s Messeenger said, “There will befall my Ummah exactly (all those) evils which befell the people of Isra'il, so much so that if there was one amongst them who openly committed fornication with his mother there will be among my Ummah one who will do that, and if the people of Isra'il were fragmented into seventy-two sects my Ummah will be fragmented into seventy-three sects. All of them will be in Hell Fire except one sect." They (the Companions) said: "Allah's Messenger, which is that?" Whereupon he said: "It is one to which I and my companions belong.”
Ibn Majah Book 36, Hadith Number 3992:
Auf ibn Malik reported that Allah’s Messenger said, "The Jews were divided into seventy one parts but only one part will be in the Paradise and seventy parts will be in the Fire; the Christians were divided into seventy two parts (out of which) seventy one parts will enter the Fire and only one part will be admitted in the Heaven. By Him in whose Hand Muhammad's life lies, my Ummah will certainly be divided into seventy three sections. Only one section will be admitted in the Heaven and seventy two sections will be in the Fire." He was asked, "Allah's Messenger, whom of them are (in the Heaven)?" He said, "Al-Jama'a."