Answer:
Around 600+ AD
The first mesaage that Muhammad received was that allahtold him that you are my prophet and you will spread Islam
the allah is one and muhammad is the messanger of allah
because prophet Mohammad [saw] is the messanger of Allah
There is no God other than Allah and Muhammad is the messenger of Allah
there is no God but Allah and Muhammad (PBUH) is messenger of Allah and people can go Heaven by submitting to Allah
messenger of Allah , sent to deliver the message of Islam
To believe in, obey & worship the only ONE God "Allah",with nothing associated to Him at all, no parents, no son, no partner, no similar.
In Islam, Muhammad is considered the last prophet and messenger of Allah. He received revelations from Allah which form the basis of the Quran, the holy book of Islam. Muslims believe that Muhammad conveyed Allah's message to humanity and served as a role model for how to live a righteous life according to the teachings of Islam.
Prophet Muhammed had received a message from ALLAH, and from that day on it spread.
Muhammad PBUH is the last ,the greatest & the most important prophet. Also, He is the best human ever & forever. He was chosen by the Almighty Allah to convey the message of Islam, the last & universal message from Allah to the mankind. For more information, refer to the related question below.
Prophet Muhammad (Peace Be Upon Him) is messenger of Allah. Allah sent him down to Earth to give the message to mankinds about Islam in order to worship the one and only God which is Allah, the Almighty and that we all can have the opportunity to do good deeds as we are striving Allah's rewards in the Hereafter which is Paradise that is known as Heaven.
The message to surrender to Allah's will , the one and only one God, was received by Muhammad from God through God revelation of Quran to him through the Angel Gabriel (Jibril) that started in year 610 AD through the year 632 AD (year of prophet Muhammad (PBUH) death. This mesaage is called Islam.