Abdullah bin `Amr bin Al-`as (May Allah be pleased with them) reported: The Prophet (PBUH) said, "(Of the) major sins are: to ascribe partners to Allah, disobey parents, murder someone, and to take a false oath (intentionally)".[Al-Bukhari].
There are many more major sins which have been enlisted and discussed at length by Muhaddathun in independent volumes, such as Az-Zawajir `an iqtraf-al-Kaba'ir, Kitab-al-Kaba'ir by Adh-Dhahabi. This Hadith mentions some of the major sins enumerated by the Prophet (PBUH) on a particular occasion. We can also say that the sins mentioned here are some of the most serious among the major sins.