QSI: The Seerah of The Prophet #36: "Big Badr and Little Badr"

"In all campaigns procurement of information is the first step towards victory. Unless the commander of an army is aware of the strength of the enemies, the point of their centralization and the morale of their soldiers, it is very likely that he may be defeated in the very first encounter.

One of the praiseworthy policies adopted by the Prophet in all the battles was that he used to collect information about the strength of the enemy and his location.  According to Allamah Majlisi the Prophet sent Adi 2 or 3 of his companions to collect information about the route and itinerary of the caravan, the number of its guards, and the nature of their merchandise.

As Quraysh had confiscated the property of Muslim Muhajirs residing in Madina, it was only appropriate that the Muslims should also confiscate their merchandise and if they persisted in withholding the property of the Muhajir Muslims on account of their enmity and obstinacy, the Muslims should, as a retaliatory measure, divide their merchandise amongst themselves as war booty.

Hence, the Prophet turned to his companions and said: "O people! It is the caravan of Quraysh. You can go out of Madina to take possession of the property of Quraysh. It is possible that your condition may improve".

In the circumstances the Prophet left Madina with 313 men in the month of Ramadan of the second year of migration to confiscate the property of Quraysh encamped by the side of the well of Badr."

http://www.al-islam.org/the-message-ayatullah-jafar-subhani/chapter-30-battle-badr