The Command for Sincerity in Worship

Allah said

﴿قُلْ إِنَّ صَلاَتِى وَنُسُكِى وَمَحْيَاىَ وَمَمَاتِى للَّهِ رَبِّ الْعَـلَمِينَ ﴾

(Say: “Verily, my Salah, my sacrifice, my living, and my dying are for Allah, the Lord of the all that exists.”) 

Allah commands the Prophet to inform the idolators who worship other than Allah and sacrifice to something other than Him, that he opposes them in all this, for his prayer is for Allah, and his rituals are in His Name alone, without partners. Allah said in a similar statement,

﴿فَصَلِّ لِرَبِّكَ وَانْحَرْ ﴾

 (Therefore turn in prayer to your Lord and sacrifice.) ﴿108:2﴾, meaning, make your prayer and sacrifice for Allah alone. As for the idolators, they used to worship the idols and sacrifice to them, so Allah commanded the Prophet to defy them and contradict their practices. Allah, the Exalted, commanded him to dedicate his intention and heart to being sincere for Him alone. Mujahid commented,

﴿إِنَّ صَلاَتِى وَنُسُكِى)

(Verily, my prayer and my Nusuk…) refers to sacrificing during Hajj and `Umrah.

Ref: Tafseer Ibn Kathir