Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) said: "When one of you prays and takes off his sandals, let him not cause harm to anyone with them; let him place them between his two feet, or pray in them."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4260