It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) would go out and urinate, then perform tayammum with earth. I would say: O Messenger of Allah, the water is close to you. He (peace and blessings be upon him) would say: "Perhaps I may not reach it."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12931