The Obligation of Tawheed

Know, may Allāh bless you, that Tawḥīd is the foundation of the religion; and that none of the pillars of the religion - from Prayer, giving the Zakât, Fasting in Ramadan and Hajj - will be accepted except with Tawheed. Just like the prayer cannot be called prayer without Wudūʾ, worship cannot be called worship except with Tawheed.