Question Summary:
How old was Usamah ibn Zayd (radhiyAllah ‘anhu)when the Messenger of Allah appointed him as the commander of the army and instructed him to go to Shāam?

Question Detail:

Is it aunthentic that usamah bin zaid was 18 years old youth when the prophet ordered him to command an army in Ghazwah? Which ghazwah was this? Was usamah the adopted son of the prophet?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
‘Allāmah Ibn al-‘Athīr writes, “The Messenger of Allah e appointed Usmāh ibn Zayd as the commander of the army at the age of 18.” He further writes, “As for Usāmah ibn Zayd, the Messenger of Allah appointed him as the commander of the army and instructed him to go to Shām.”[1]
Although Usamāh (radhiyAllah ‘anhu) was not the adopted son of Rasūlullah e, he was the son of Zayd ibn Hāritha (radhiyAllah ‘anhu), who was the adopted son of Rasūlullah e.[2]
 
 
And Allah Ta’āla Knows Best
Muntasir Zaman
Student Darul Iftaa
USA
Checked and Approved by,
Mufti Ebrahim Desai.