Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) reports this as a marfu' hadith: The Prophet (peace and blessings be upon him) said: "A person with ordinary clothing, who is paid no attention, may be such that if he swears an oath by Allah, Allah Almighty fulfils it for him."
Imam al-Bazzar recorded it, and its narrators are the narrators of the Sahih, except Jariyah bin Haram, and Ibn Hibban declared him trustworthy despite his weakness.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الزهد / 17919