What is Islamic Tawheed (Oneness of Allah)?
It means devoting worship to him alone like supplication, vow, judgment.
Evidence from the Noble Qur'an
{So know (O Muhammad) that there is no God except Allaah}, {Soorah Muhammad, verse 19]
Evidence from the authentic Sunnah
((Let the first thing you invite them to do is to testify that none has the right to be worshipped but Allaah)), [Transmitted by al-Bukhaaree and Muslim]