Dhul-Qi’dah is taken from the word "qa'ada" which means to sit. During its time, people used to stop their business activities and sit and prepare for the Pilgrimage.
As well as being the first of the four sanctified months, Dhul-Qa’dah is also one of the months of Hajj (see Shawwal). Despite the significance of this month, no specific acts of worship are prescribed for it.
The Battle of 'Khandaq (trench) or Ahzab' took place in the year 5 AH
The Truce of Hudaubiyah in the year 6 AH
'Bay'at-e-Rizwaan' (The oath of allegiance named Rizwaan) in the year 6 AH
The Holy Prophet (SAW) and his Companions returned to Makkah for Umrah in the year 7 AH
Ref : http://www.ciibroadcasting.com/index.php/islam/months-in-islam