Did the Prophet PBUH attack Bani Mustaliq because they are Jews?
The battle between Muslims and Bani Mustaliq was not due to ethnicity. In fact, Bani Mustaliq is one of the Arab tribes and not Jews. Islam calls its ummah towards harmony in dealing with different races and cultures. However, the battle happened because a threat was given from the head of Bani Mustaliq which is al-Harith bin Abu Dhirar who wanted to defy the Prophet PBUH and the Muslims.
Al-Waqidi mentioned that Bani Mustaliq branches from Bani Khuza’ah. So, their dwelling was located near the valley of al-Muraisi’ which is located inside the territory of Bani Khuza’ah. (See al-Maghazi li al-Waqidi, 1/404)
The battle of Bani Mustaliq happened in the month of Sha’aban on the fifth hijrah year (there is an opinion which states that it was the sixth of hijrah). The cause of the battle is due to that the Prophet PBUH received information that the leader of Bani Mustaliq which is al-Harith bin Abu Dhirar called his tribe and the Arabs surrounding them to attack the Prophet PBUH and the Muslims. (See al-Maghazi li al-Waqidi, 1/404)
Then, the Prophet PBUH sent Buraidah bin al-Hasib al-Aslami to verify the authenticity of the information. Buraidah disguised as a follower of al-Harith bin Abu Dhirar to get clear info on the strategic plan for the attack. After he verified the info, he then came back to meet the Prophet PBUH and informed as well as verifying the news he got from his meeting with al-Harith bin Abu Dhirar. (See al-Maghazi li al-Waqidi, 1/404-405)
Two days reaching the end of Sha’ban, the Prophet PBUH gathered the Companions and rushed out to set an attack. (See al-Rahiq al-Makhtum, 1/298)
At the same time, large numbers of those who followed were among the munafiq whereas they never followed any expedition before. Therefore, these people actually only wanted the booties of the war (ghanimah) and not to help the Muslims. (See Fiqh al-Sirah, 298)
Al-Harith bin Abu Dhirar also sent a spy to investigate the strength of the Muslims. However, the spy was captured by the Muslims and killed. Al-Harith bin Abu Dhirar and his army felt very scared when they got to know that the Prophet PBUH and the Muslims were coming towards them. Besides, the fear also due to the killing of the spy sent by him. Several Arab tribes left al-Harith and his army. (See al-Rahiq al-Makhtum, 1/299)
Lastly, the Prophet PBUH and the Muslims reached Muraisi’. According to historians, Muraisi’ is a coastal area owned by Bani Mustaliq in Qudaid. The Prophet PBUH lined up his people and the Muslims got ready for the war. Then, the Muhajirin flag was given to Saidina Abu Bakar R.A while the Ansar flag was given to Sa’ad bin Ubadah. Not long from that, those two opponents took off their arrows, battling one another, and the Prophet PBUH commanded the Muslims to attack all at once. This caused al-Harith and his team to successfully be defeated. Most of Al-Harith’s men were killed, women and children were made captives while farm animals were seized. Whereas only one person among the Muslims was killed. This is as what was mentioned by the historian and scholars in civilizations. (See al-Rahiq al-Makhtum, 1/299)
Then, there was also another event that happened during the battle of Bani Mustaliq which is a slander (ifk) spread by Abdullah bin Ubai bin Salul. He was the leader of the munafiq at that time. He slandered Sayyidatina Aisha R.Anha by cheating on the Prophet PBUH behind his back. For further explanation on this slander (ifk), we already explained it in BAYAN LINNAS SERIES 181: THE EVENT OF AL-IFKI (SLANDER) TOWARDS AISHA R.ANHA: LESSONS AND GUIDANCE IN FACING CURRENT FITNAH.
Based on the analysation of history books, the main reason the Prophet PBUH attacked Bani Mustaliq is because they prepared war weapons as well as calling all other Arabs surrounding them to plan an attack towards the Prophet PBUH and the Muslims. Counter-attacks from the Muslims were not due to the sentiment of nationality. However, it was due to the threat received from Bani Mustaliq. In fact, Bani Mustaliq is one of the Arab tribes and not Jews. Islam is a religion that hates his ummah to be racists (‘asabiyyah) towards other people. This is among the characters hated by the Prophet PBUH himself.