There are some days and night that God has made special and gave a great position as they were linked to some events that have affected the march of Islam and Muslims, among of which is the day of the appointment to the Prophetic mission which falls in the 27th of Rajab. It is one of the greatest feast even it wasn't called an Eid. It is the day of the start of the revelation of the Mohammadian Islamic message from the Almighty God through the great angel Gabriel to convey His message to the noble and great Messenger who was sent as mercy to the worlds, so the light of goodness, faith and guidance shines. The beginning of the Prophetic mission of Mohammed (prayers and Allah's peace be upon him and his holy Household) formed a limit line between the ignorance time [Jahiliyah] and the Islam, and people were brought out from the delusion darknesses into the light of guidance and faith.
Thirteen years before the blessed Prophet's migration, in the mountain of Noor [light] in the east of Mecca at the left when going to the Mount Arafat, the first divine word delivered by the Trustworthy Spirit to the Holy Prophet Mohammed (prayers and Allah's peace be upon him and his holy Household) was "READ!" [Iqra'] by which he announced the start of the last divine message that will be the Seal of all previous prophetic messages. The first believer of this day, the supporter and the defender of this message, the brave boy, Imam Ali (peace be upon him). So the sun of Islam rose to displace the delusion and darkness from the face of the whole humanity. The first people that the Holy Prophet (prayers and Allah's peace be upon him and his holy Household) called them to Allah's path were his cousin Ali Ibnu Abi Taleb (peace be upon both of them) and he was then only ten years old, and his faithful wife Khadija (peace be upon her) who have straightforward believed in him and were the first nucleus of the great Islamic mission.
The Almighty God has prepared His noble Messenger (prayers and Allah's peace be upon him and his holy Household) so he is ready to carry the Islamic message and the great trust to rescue the humanity from the loss of misguidance and the nightmare of ignorance. At the age of forty, the Almighty ordered him to start conveying his message, which wasn't an easy responsibility as he (prayers and Allah's peace be upon him and his holy Household) has said: "No prophet was harmed like I was." nevertheless he continued to spread his message and to call to Islam, until crowds entered into the religion of Allah.
The divine message was launched then to herald a new era which miracle is the "word" that the Almighty ensure to preserve. This religion was spread thanks to the blessings of the morals of the Holy Prophet (prayers and Allah's peace be upon him and his holy Household) not through the swords of those who came after him, according to plaintiff's' allegations. The real Muslims were then those who embraced this religion without any other intention or any kind of hypocrisy, to constitute a state which horizons are from China to Andalusia.
27th Rajab is a highly blessed night / day called ‘laylat al-mab`ath’, which stands for the beginning of the Holy Prophet’s Mission of promulgating the true religion of Almighty Allah On this day, the Holy Prophet (Allah's prayers be upon him and his holy Household) was appointed for conveying the Divine Mission of Almighty Allah when Archangel Gabriel first came to him with the Divine Revelation.
It is recommended to have Ghusl (bath) on this day. And to observe Fasting. This day is one of the four days that are specified for highly recommended fasting during the whole year. The reward of observing fasting on this day is mentioned to be equal to seventy years fasting.
It is recommended to repeat very frequently the Salawat i.e. sending blessings upon Prophet Mohammad and his Household.