Year 6 AH (628 AD)
Banu sulaym (or Banu saleem – salim) had plotted attempts to attack Muslims before this. In fact, on some of these incidents they killed many Muslims. This expedition to Al-Jumum (Al-Jamum) led by Zaid ibn Haritha was most probably continuation of ongoing Battles against the enemy (Banu Sulaym).
Imam Zaid Shakir:
“Not Only did the Prophet love Zayd b. Haritha, he trusted him with the command of many of the expeditionary forces that took the field in the early days of Islam. In fact, Zayd b. Haritha was the most prominent Muslim commander during that time. He led the expedition at al-Qarada in the Najd, to Bani Sulaym at al-Jamum…” 
“In the year six AH, in Muharram, Ibn Unays led an expedition to Sufyan b. Khalid b. Nubayh… the fourth, by Zayd b. Haritha against Bany Sulaym at al-Jamum (Which lies between batn Nakhl and al-Naqra). …” 
There are many historical evidences wherein the Banu Sulaym tribe were arch-enemies of the Muslims and had a numbers of times attacked Muslims. This is preceding the expedition of Zaid ibn Haritha to Al-Jumum (Al-Jamum). Click on the links below for more information:
1. Bir Ma’una
2. Al Kudr Invasion
3. Invasion of Bahran
4. Battle of Khandaq
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 Scattered Pictures: Reflections of an American Muslim : an Anthology of Essays [2005, Zaytuna institute] By Imam Zaid Shakir, page 72
 The Life of Muhammad: Al-Waqidi’s Kitab al-Maghazi [Translator: by Rizwi Faizer] page 5