The Prophet Muhammed (p) sent Umar Ibn Al-Khattab with thirty of his companions, against a branch of the Hawazin, at Turabah (Turbah). Umar Ibn Khattab travelled through the land in the night and hid in the day. When the Muslims arrived at the location, the Banu Hawazin all ran off, most probably received news of Umar Ibn Khattab, they made a escape.
Kitab al-tabaqat al-kabir – Ibn Sa’d:
“THE SARIYYAH OF IBN AL-KHATTAB, AGAINST TURABAH
Then (occurred) the sariyyah of Umar Ibn al-Khattab, against Turabah, in Sha’ban of seventh year from the hijrah of the Apostle of Allah. They (narrators) said: The Apostle of Allah sent Umar ibn Al-Khattab with thirty men against a branch of Hawazin, at Turabah, which lies in the terrirtory of al-Abla, at (a distance of) four nights (journey) from Makkah on the way to San’a and Najran. He (Umar) set out and a guide of Banu Hilal set out with him. He marched by night and remained concealed in day. The news reached the Hawazin, so they fled. Umar Ibn al-Khattab arrived at their place. There he met no body; so he returned to al-Madinah.” 
“THE EXPEDITION OF UMAR B. AL-KHATTAB TO TURBA
Usama b. Zayd b. Aslam related to us from Abu Bakr b. Umar b. Abd al-Rahman, who said: The Messenger of God sent thirty men with Umar to Ajuz Hawazin in Turba. Umar set out with a guide from the Banu Hilal. They marched by night and hid by day, but news came to the Hawazin and they fled. Umar came to their locality but did not meet even one of them. He turned to return to Medina, and when he was passing al-Najdiyya, and he was at the wall, the Hilali said to Umar b. al-khattab, ‘would you like to have another group that I have left, from Khath’am? They came walking, for their land is dry.’ Umar said, ‘The Prophet did not command me about them. Indeed, he commanded me to stay and fight the Hawazin in Turba.’ And Umar returned to Medina.” 
Al-Sira Al-Nabawiyya – Imam Ibn Kathir:
“THE EXPEDITION OF UMAR B. AL-KHATTAB, TO TURBA, IN HAWAZIN TERRIRTORY, FOUR MILES BEYOND MECCA.
Then al-Bayhaqi related, through al-Waqidi with the lines of tradition given by him, that the Messenger of God (SAAS) sent Umar b. al-Khattab, along with 30 riders and a guide of Banu Hilal. They travelled by night and kept concealed by day. When they reached the enemy territory, they fled and so Umar returned to Medina. …” 
Dr. Shawqi Abu Khalil:
“The expedition of Umar ibn al-Khattab to Turabah in Sha’ban 7 AH. He led thirty men to the tribe of Hawazin, who fled when they learned of his approach, so he returned to al-Madinah.” 
The expedition of Umar ibn al-Khattab doesnt specifically tell us why Umar Ibn Khattab was sent, the wordings used in the reports suggest and hint to us that they were enemies of the Muslims. Take for example, why would Umar Ibn Khattab and his Companions travel in night, but hide through the day unless they, the Hawazin had attacked and killed Muslims before? Moreover, if they weren’t guilty of doing anything before, why would they run away?
Furthermore, the Prophet (p) would never fight anyone who was at peace with the Muslims i.e., if they didn’t fight against the Muslims, they were left alone. The Prophet (p) prayed and urged God that his aggression be only against those who persecute Muslims. Riyad as-Salihin:
“O God, apportion to us such fear as should serve as a barrier between us and acts of disobedience; and such obedience as will take us to Your Jannah; and such as will make easy for us to bear in the calamities of this world. O God! let us enjoy our hearing, our sight and our power as long as You keep us alive and make our heirs from our own offspring, and make our revenge restricted to those who oppress us, and support us against those who are hostile to us let no misfortune afflict our Deen; let not worldly affairs be our principal concern, or the ultimate limit of our knowledge, and let not those rule over us who do not show mercy to us).” (Riyad as-Salihin Book 5, Hadith 834)
From the evidences we gather that the Prophet (p) sent out Umar Ibn Khattab against the branch of Hawazin as a result of the ongoing hostilities against the Muslim community.
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 Kitab al-tabaqat al-kabir, by Ibn Sa’d, volume 2, page 146
 The Life of Muhammad: Al-Waqidi’s Kitab Al-Maghazi [Translator Rizwi Faizer], page 335
 Al-Sira Al-Nabawiyya | The Life of the Prophet by Imam Ibn Kathir, volume 3, page 300
 Atlas on the Prophet’s Biography – Places, Nations, Landmarks (Al-sirah Al-Nabawiyah) by Dr. Shawqi Abu Khalil, page 205