News reached Prophet Muhammed (p) that Banu Sa’d bin Bakr tribe were planning to help the Jews of Khaybar, who were the enemy of Mohammed, to attack the Muslim community. The Prophet in turn sent out his companions to counter them.
Kitab al-tabaqat al-kabir – Ibn Sa’d:
“THE SARIYYAH OF ALI IBN ABI TALIB AGAINST BANU SA’D IBN BAKR AT FADAK
Then (occurred) the Sariyyah of Ali Ibn Abi Talib on Banu Sa’d Ibn Bakr at Fadak, in Sha’ban of the sixth year from the hijrah of the Apostle of Allah. They (narrators) said: The news reached the Apostle of Allah that their forces, had collected and intended to assist the Jews of Khaybar. The Apostle of Allah sent Ali Ibn Abi Talib with one hundred men. He travelled in the night and remaind in concealement in the day; he reach al-Hamaj, which was a spring between Khaybar and Fadak. … Their chief was Wabr Ibn Ulaym. …” 
“In this year a raiding party led by Ali b. Abi Talib went to Fadak in Sha’ban. … Ali b. Abi Talib set out for Fadak with a hundred men against a clan of the Banu Sa’d b. Bakr. This was because the Messenger of God had received information that a force of theirs intended to aid the Jews of Khaybar. Ali travelled toward them by night and lay in wait during the day. He captured a spy, who confessed to them that he had been sent to Khaybar to offer the people their aid on condition that they would give them the date harvest of Khaybar.” 
“THE EXPEDITION OF ALI B. TALIB TO THE BANU SA’D IN FADAK
… The Messenger of God sent Ali with a hundred men to confront the Banu Sa’d in Fadak for it had reached the Messenger of God that they had a group desiring to help the Jews of Khaybar. Ali marched by night and hid by day until he reached al-Hamaj. He captured a spy and said, ‘Who are you? Do you have information of what has happened to the group of the Banu Sa’d?’ The spy replied, ‘No, I do not have any information about it.’ But they were firm with him and he confirmed that he was a spy of the Banu Sa’d sent to Khaybar to PROPOSE TO THE JEWS OF KHAYBAR THAT THEY WOULD HELP THEM if the Jews of Khaybar would provide them dates just as they did for others who helped them. They said to him, ‘Where are the people?’ He replied, ‘I left them; they gathered among two hundred men, and their leader is Wabr b. Ulaym.’ …” 
“Delegations and Expeditions following Al-Muraisi‘ Ghazwah
In the same month and year, ‘Ali bin Abi Talib was despatched at the head of a platoon to the habitation of Bani Sa‘d bin Bakr in a place called Fadk. Prophet Muhammad [pbuh] had been reported that those had rallied ranks to support the Jews. The Muslim fighters used to march in the day and lurk at night. On their way, they captured an enemy scout who admitted being sent to Khaibar tribe, to offer them support in return for their dates. ‘Ali and his companions raided their encampment, captured five hundred camels and two thousand goats, but Banu Sa‘d, with their chieftain Wabr bin ‘Aleem had fled away.” 
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 Kitab al-tabaqat al-kabir, by Ibn Sa’d, volume 2, page 110 – 111
 The History of Al-Tabari: The Victory of Islam: Muhammad at Medina A – [Translator: Michael Fishbein], volume 8, page 95
 The Life of Muhammad: Al-Waqidi’s Kitab Al-Maghazi [ Translator: Rizwi Faizer], page 276
 Sealed Nectar (‘Ar-Raheeq Al-Makhtum’), By Safiur-Rahman Al-Mubarakpuri, page 211