(Hood) 11 : 26
أَنْ لَا تَعْبُدُوا إِلَّا اللَّهَ ۖ إِنِّي أَخَافُ عَلَيْكُمْ عَذَابَ يَوْمٍ أَلِيمٍ
"That you do not serve except Lord Allah; indeed, I fear for you the punishment of a painful day".
Adhikr is the only Book revealed from the first Messenger, Noah, to the last Messenger, Muhammad. It is revealed to remind mankind that there is no deity except Lord Allah and that you should serve Him alone, as explained in verses 4:63-64. See explanation 7:59-64 and 11:2-3.