Sayyiduna Anas bin Malik (may Allah be pleased with him) says: A man entered the mosque to announce a lost item, and the Prophet (peace and blessings be upon him) said: "May you not find it."
Al-Tabarani recorded it in al-Mu'jam al-Awsat, and its narrators are thiqat (trustworthy). Al-Bazzar recorded it with a weak chain; other hadiths on this will come in the chapter on lost property.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2043