Signs of Tawhid
Allah tells us that pondering His creation will show that He exists and that He is Unique in creating it, and that there is no god nor lord besides Him.
So He says:
أولم يتفكروا في أنفسهم
Do they not reflect upon themselves!
Thinking and pondering how Allah created various things in the upper and lower realms and in the space between, realizing that this was not created in jest or in vain, but in truth, and that it will continue until an appointed time, the Day of Resurrection, as Allah says:
ما خلق الله السماوات واﻻرض وما بينهما إﻻ بالحق وأجل مسمى
Not but for just ends and for a term appointed, did Allah create the heavens and the earth, and all between them:
وإن كثيرا من الناس بلقاء ربهم لكافرون
And indeed many of mankind deny meeting with their Lord.
Then Allah tells us of the truth of the Message brought by the Messengers and how He supported them with miracles and clear signs, such as when He destroyed those who disbelieved in them and saved those who believed in them