Muhammad bin al-Ash'ath narrates from his father, from his grandfather, that the Prophet (peace and blessings be upon him) said: "Oil removes squalor (or dryness), clothing shows prosperity, and treating a servant well weakens the enemy."
Imam al-Bazzar recorded it. Its chain contains a narrator, Sulayman bin Ubaydullah Abu Ayyub al-Raqqi, and he is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب اللباس / 8584