The incident at Sawiq took place because of the continued hostilities and aggression of the Quraysh against the Muslims. When they lost at the battle of Badr, Abu Sufyan couldn’t accept it. Not long after the battle of badr, he set out with his companions, murdered two innocent men and set fire to houses and the corn fields. Upon the Prophet receiving news of this he dispatched companions to go in pursue of these criminals.
“THE RAID OF AL-SAWIQ
then Abu Sufyan b. Harb made the raid of Sawiq in Dhu’l-Hijja. The polytheists were in charge of the pilgrimage that year. Muhammad b. Ja’far b. al-Zubayr and Yazid b. Ruman and one whose veracity I do not suspect from Abdullah b. Ka’b b. Malik who was one of the most learned Helpers told me that when Abu Sufyan returned to Mecca and the Quraysh fugitives returned from Badr, he swore that he would not practice ablution until he had raide Muhammad. Accordingly he sallied forth with two hundred riders from Quraysh to fulfil his vow. He took the Nejd road and stopped by the upper part of a watercourse which led to a mountain called Thayb about one post distance from Medina. Then he sallied forth by night and come to the B. al-Nadir under cover of darkness.
He came to Huyyayy b. Akhtab and knocked upon his door, but as he was afraid of him he refused to open the door, so he went to Sallam b. Mishkam, who was their chief at that time, and keeper of the public purse. He asked permission to come in and Sallam entertained him with food and drink, and gave him secret information about the Muslims. He rejoined his companions at the end of the night and sent some of them to Medina. They came to an outlying district called Al-Urayd and there they burnt some young palm-trees and finding one of the Helpers and an ally of his working the fields there, they killed them and returned. People got warning of them and sothe apostle went out in pursuit. He got as far as Qarqaratu’l-Kudr and then returned becayse Abu Sufyan and his companions had eluded him. They saw some of the provisions which the raiders had thrown away in the fields to lighten their baggage so as to get away quickly. ‘Do you hope that this will count (with God) in our favour as a raid?’ and he replied, ‘yes’.” 
Kitab al-tabaqat al-kabir – Ibn Sa’d:
“GHAZWAH OF AL-SAWIQ
Then (occurred) the ghazwah of the Prophet, known as ghazwah al-Sawiq (lit. gruel of parched barley). The Apostle of Allah emerged on Sunday, the twenty fifth of Dhu al-Hijjah after the commencement of the twenty-second month after his hijrah. He appointed Abu Lubabah Ibn Abd al-Mundhir al-Amiri as his vicegerent in al-Madinah. (The course of this ghazwah) was that Abu Sufyan Ibn Harb had made the use of oil unlawful (for himself) after their (polytheists) retreat from Badr to Makkah until they had taken revenge from Muhammad and his companions. So he set out at the head of two hundred persons, according to the version of al-Zuhri, and according to the version of Ibn Ka’b at the head of forty.
They marched to al-Najdiyah and came to Banu al-Nadir in the night. They knocked at the door of Huyayyi Ibn Akhtab to gather information about the Apostle of Allah and his companions. He refused to open the door. They knocked at the door of Sallam Ibn Mishkam who opened the door, feasted them, offered them drink and supplied information about the Apostle of Allah. When it was morning, Abu Sufyan Ibn Harb set out and went to al-Urayd, about three miles from al-Madinah. There he killed a man of the Ansars and his servant and put a few houses and grass to fire. … Then he turned his back and fled away. The news reached the Apostle of Allah. He called his companions and set out at the head of two hundred persons from among the Muhajirs, and the Ansars in their pursuit. Abu Sufyan and his companions were throwing bags of gruel of parched barley, their general provisions, to render themselves light. The Muslims seized them (Bags) and so it has come to be called ghazwah al-Sawiq. They did not encounter them (Muslims). The Apostle of Allah returned to al-Madinah from where he had been absent for five days.” 
“… In order to fulfil his vow, he set out at the head of two hundred horsemen of Quraysh and took the Najdi route, halting in the upper part of Qanat by a mountain called Tayt (variant Thayb), a stage or so from Medina. Then he set out by night and came, while it was still night, to the Banu al-Nadir. He went to Huyayy b. Akhtab and knocked at his door, but Huyayy refused to open up, being afraid of him. Then he went to Sallam b. Mishkan, who was the chief of al-Nadir at that time and their treasurer, and asked to be allowed to enter. Sallam did so, provided him with food and drink, and gave him confidential information about the Muslims. Towards the end of the night, Abu Sufyan left and returned to his companions, then sent some men of Quraysh into Medina. These went to a district called al-Urayd, set fire to the date gardens there, and killed a man of the Ansar and his confederate whom they found in arable ground belonging to the man.
After that, they left and went back. The Muslims caught sight of them, however, and the Messenger of God set out in pursuit. He went as far as Qarqarat al-Kudr but then turned back, because Abu Sufyan and his companions had eluded them. The Muslims saw provisions which these had discarded in the fields in order to lighten their load and escape. …” 
“THE RAID OF AL-SAWIQ
The raid of al-Sawiq was in Dhu l-Hijja, the twenty-second month AH. The Prophet went out on Sunday, the fifth of Dhu l-Hijja. He was absent for five days. … When the polytheists returned to Mecca from Badr, Abu Sufyan forbade oil for himself until he took his revenge on Muhammad and his companions for those whom they had taken from his people. He went out with two hundred riders, according to al-Zuhri, but according to the traditions of Ibn Ka’b with four hundred riders, and took the road to al-Najd.
They came to the Banu Nadir by night and knocked at Huyayy b. Akhtab’s and inquired of news of Muhammad and his companions. Huyayy refused to open to them so they knocked on Sallam b. Mishkam’s door, and he opened his doors for them and was hospitable to them. He gave Abu Sufyan to drink and news of Muhammad and his companions. At daybreak Abu Sufyan left, passing through al-Urayd.
Finding a man from the Ansar with an employee of his in his fields, he killed them and burned their houses at al-Urayd and burned their field. … Then he went swiftly, fearing to be found. This reached Muhammed and he selected his companions and they went out in Abu Sufyan’s tracks. …” 
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 Ibn Hisham , Ibn Ishaq, [Alfred Guillaume (translator)]. The life of Muhammad: a translation of Isḥaq’s Sirat rasul Allah. page 361.
 Kitab al-tabaqat al-kabir, By Ibn Sa’d, volume 2, page 33–34
 The History of al-Tabari: The Foundation of the Community: Muhammad. Volume 7, page 90
 The Life of Muhammad: Al-Waqidi’s Kitab Al-Maghazi [Translator: Rizwi Faizer], page 90