Qatadah says: I heard Anas bin Malik (may Allah be pleased with him) narrating that there was a panic in Madinah, so the Prophet (peace and blessings be upon him) borrowed a horse from Abu Talhah (may Allah be pleased with him), named al-Mandub, and he (peace and blessings be upon him) rode it. When he returned, he (peace and blessings be upon him) said: "We did not see anything, and we found it (the horse) to be a sea."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السبق والرمي / 19803