Is the aforementioned hadith, narrated by Ibn Mas'ud from the Prophet (peace and blessings be upon him), which describes the last man to enter Paradise, an authentic hadith?

The scholars of Hadith terminology stated that what the two Shaykhs (Al-Bukhari and Muslim) narrated is considered authentic, or highly likely to be authentic. No one is known to have disagreed with the authenticity of this hadith.