The interception of the caravan in Najd (Nejd) took place in the 3 AH (624 AD).
The Quraysh sent Safwan Ibn Umayyah to Syria for trade. In reference to Quraysh, they had persecuted and murdered many Muslims. As a result of these actions of the Quraysh, the Muslims fought back against them. As a consequence of the Quraysh’s continued war against the Muslims, they had in turn started attacking the wealth of the Quraysh, to weaken them economically, so as to make to unable to buy horses, swords, or any other military instruments to fight the Muslims.
Some critics have argued that the Muslims raided Quraysh’s caravan so to make themselves rich. If this was the case, then the Quraysh’s caravan wouldn’t have been the only target. They would’ve attacked every caravan. As history is witness, only the Quraysh were touched. The claim about Muslims making themselves ‘rich’ has no truth to it.
The Muslims attacked the Quraysh’s caravan at a time of war. They were attacked for two reasons, (1) as explained previously, weaken the Quraysh’s military money. (2) When the Muslims fled from persecution from Makkah, the Quraysh robbed their properties and household of the Muslims. The Muslims were regaining things that were theirs in the first place (read more about here: ‘Property Of Muslims Stolen – Robbed By Quraysh In Makkah?‘).
“THE RAID OF ZAYD B. HARITHA TO AL-QARADA
The story of the foray of Zayd who captured the caravan of Quraysh, in which was Abu Sufyan b. Harb, when the Apostle of sent him to al-Qarada a watering place in Najd, is as follows: Quraysh were afraid to follow their usual route to Syria after what had happened at Badr, so they went by the Iraq route. Some of their merchants went out, among whom was Abu Sufyan, carrying a great deal of silver which formed the larger part of their merchandise. They hired a man from the B. Bakr b. Wa’il called Furat b. Hayyan to conduct them by that route. The Apostle duly sent Zayd, and he met them by that watering place and captured the caravan and its contents, but the men got away. He brought the spoil to the Apostle. …” 
Kitab al-tabaqat al-kabir – Ibn Sa’d:
“Then (occurred) the Sariyyah of Zayd Ibn Harithah against al-Qaradah, and it was on 1 Jumada al-Akhirah, after the commencement of the twenty-eighth month from the hijrah of the Apostle of Allah. It was the first Sariyyah under the leadership of Zayd. Al-Qaradah is a tract of Najd lying between al-Rabadhah and al-Ghamrah in the territory of Dhat Irq. The Apostle of Allah despatched him to intercept the caravan of the Quraysh in which there were Safwan Ibn Umayyah, Huwaytib Ibn Abd al_uzza and Abd Allah Ibn Abi Rabi’ah. … Their guide was Furat Ibn Hayyan al-Ijli who led them to Fhat Irq by way of Iraq. The report of their affair reached the Apostle of Allah. He despatched Zayd Ibn Harithah at the head of one hundred horsemen, who intercepted (the caravan) and got it. The chiefs of the people made good their escape. …” 
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 Ibn Ishaq’s Sirat Rasul Allah – The Life of Muhammad [Translated: A. Guillaume], page 364
 Kitab al-tabaqat al-kabir, Ibn Sa’d, volume 2, page 41 – 42