The best Time to perform 'Umrah is during Ramadhan
Question :
Is there any specific virtue that is confirmed for performing 'Umrah during the months of Hajj that is different from its virtue in other months?
Answer:
The best time to perform 'Umrah is during the month of Ramadhan. This is due to the Prophet's statement:
"An 'Umrah in Ramadhan is equal to a Hajj.”
The authenticity of this Hadith is agreed upon and in another narration in Al-Bukhari the wording is:
"Is equivalent to a Hajj (performed) with me."
And in Muslim one wording states:
"Is equivalent to a Hajj or a Hajj (performed) with me."
It has been reported like this with doubt. This means a Hajj performed with him. Then after that, the 'Umrah performed in Thul-Qa'dah, because all of the Prophet's 'Umrahs were in Thul-Qa'dah, and indeed Allâh said:
"Indeed there is an excellent example for you in the Messenger of " Allah (Muhammad)."
And success is from Allâh.
Source:
Ash-Shaykh Ibn Baz
Fatawa Islamiyah, Vol. 4 Pages 291-292