Glad tidings during digging Al-Khandaq (the trench)
29-4-2007 | IslamWeb
Question:
When the rock was hit by the Prophet, sallallaahu alayhi wa sallam, in the Battle of the Trench, what were the sparks for each area that will be conquered, and who were the ones that conquered them?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It is confirmed that An-Nasaa'i and others 
reported that when the Companions 
were digging Al-Khandaq (i.e. the trench), they found a rock which was too immense for their spades to break up. So, they sought the help of the Prophet 
.
He struck the rock three times, and each time he would strike it, a bright light would spark – and in another narration it was like a light in the middle of a dark night. This is evidence that the three sparks came up with each strike. He took the spade, and struck the rock uttering: "Allaahu Akbar (i.e. Allaah is The Greatest)! The keys of ancient Syria are granted to me, I swear by Allaah, I can see its palaces at the moment”; on the second strike he said: "Allaahu Akbar (i.e. Allaah is The Greatest), Persia is granted to me, I swear by Allaah, I can now see the white palace of Madain"; on the third strike he said: “Allaahu Akbar (i.e. Allaah is The Greatest), I have been given the keys of Yemen, I swear by Allaah, I can see the gates of Sana' while I am in my place.” [Ahmad].
All these countries were conquered exactly as the Prophet informed us, but they were not all conquered at the same time. The first city to be conquered in Ancient Syria was Busra, it was conquered in a peace treaty during the reign of Abu Bakr 
as stated by Ibn Katheer 
. 'Umar continued its conquest and conquered Persia as well.
Ibn Sa'd when speaking about the conquests of 'Umar said, “He conquered the entire Iraq, Azerbaijan, Al-Basra, Persia, and ancient Syria.”
As regards Yemen, Islam spread in it during the reign of the Prophet and Mu'aath ibn Jabal was sent there by the Prophet to rule over it. Then, Al-Aswad Al-'Ansi took power over it until Fayrooz killed him during the last period of the reign of the Prophet .
Allaah Knows best.