Sayyiduna Anas bin Malik (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) used to take his midday rest at the house of Sayyidah Umm Sulaym (may Allah be pleased with her), and he (peace and blessings be upon him) would pray on a mat. He (peace and blessings be upon him) used to sweat a great deal. Sayyidah Umm Sulaym (may Allah be pleased with her) would collect the sweat from the mat and put it in a bottle of perfume, and he (peace and blessings be upon him) would pray on the mat.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4196