Question: Does performing ‘Umrah (lesser pilgrimage) during the months of Hajj have any particular virtue different from performing it in other months?
Answer: The best month to perform ‘Umrah is during Ramadan, for the Prophet (peace be upon him) said: ‘Umrah (performed) in Ramadan is equal to Hajj (in reward).(Agreed upon its authenticity by Imams Al-Bukhari and Muslim) According to another narration by Al-Bukhari: It is equivalent to performing Hajj with me. According to the narration by Muslim: It is equivalent to Hajj or Hajj performed with me (in reward). This means that it is equivalent to Hajj or (indicative of uncertainty on the part of the Hadith narrator) equivalent to Hajj performed with the Prophet (peace be upon him). Then, comes the ‘Umrah in Dhul-Qa‘dah, for all the ‘Umrahs which the Prophet (peace be upon him) performed took place in Dhul-Qa‘dah. Allah (Glorified be He) says: Indeed, in the Messenger of Allâh (Muhammad peace be upon him) you have a good example to follow
May Allah grant us success!
Source: Fatwas of Ibn Baz