The incident at Al-Kudr took place because the Banu Saleem and Ghatafan tribe had mobilised troops in order to attack the Muslim community.
“…he led an expedition to Qarqarat al-Kudr when he heard that the Banu Sulaym and Ghatafan were gathering. He set out from Medina on a Friday, when the sun was high in the sky, on the first day of Shawwal in the second year of the Hijraj (March 27, 624). … When the Messenger of God came to Medina from Badr, having finished with Badr at the end of Ramdan or the beginning of Shawwal, he spent only seven days in medina before leading an expedition in persons agsinst the Banu Sulaym. He got as far as one of their watering places, called al-Kudr, stayed there for three days, and then went back to Medina without any fighting.” 
Kitab Al-tabaqat Al-Kabir – Ibn Sa’d:
“GHAZWAH OF QARAQAT AL-KUDR
Between al-Ma’dan and al-Madinah there is (a distance of) eight burds (ninety-six miles). His standard was borne by Ali Ibn Abi Talib. He appointed Abd’Allah Ibn Umm Maktum his vicegerent in al-Madinah. It (report) had reached him that Banu Sulaym and Ghatafan had mobilised (their men) at that place. He marched towards them but he did not find anyone there.” 
The scouting body of Madinah reported that Banu Saleem of Ghatafan were engaged in mustering troops to invade the Muslims. The Prophet took the initiative himself and mounted a surprise attack on them in their own homeland at a watering place called Al-Kudr. Banu Saleem, on receiving the news, had fled before he arraived.” 
Dr. Shawqi al –Khalil:
“The campaign of Banu Sulaim in Al-Kudr in Muharram, twenty-three months after the Hijrah.
The Messenger of Allah went to confront a group of Banu Sulaim and Ghatafan, and went as far as Qarqarat Al-Kudr.” 
Shaikh Abdullah Ibn Muhammad:
“In the first days of Shawwal, seven days after the Battle of Badr, or it was said, in the middle of Muharram, in the third year, the Messenger of Allah set out for Banu Sulaim, and when he reached a watering-hole known as Qarqara Al-Kudr, which lies in flat land: Al-Kudr is a bird, so called because of its muddy-coloured plumage. … The reason for the raid was that he had been informed that at his location Banu Sulaim and Ghatafan were gathering (for an attack on Al-Madinah), so he set out for it, but he did not find anyone there.” 
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 The History of al-Tabari: The Foundation of the Community: Muhammad [Translator: William Montgomery Watt, Michael V. McDonald], volume 7, page 88
 Kitab Al-tabaqat Al-Kabir by Ibn Sa’d, volume 2, Page 34 – 35
 The Sealed Nectar: Ar-Raheeq Al Makhtoom By Safiur-Rahman Al-Mubarakpuri, page 157
 Atlas On The Prophet’s Biography Places, Nations, Landmarks – Atlas Al-sīrah Al-Nabawīyah By Dr. Shawqi al –Khalil, page 132
 Biography Of The Prophet By Shaikh Abdullah Ibn Muhammad Ibn Abdul Wahhab, volume 1,
page 469 – 470