Sayyiduna Abu Musa Ash'ari (may Allah be pleased with him) says that we were with the Messenger of Allah (peace and blessings be upon him) during Hajj. When we would ascend a height, we would say La ilaha illallah and Allahu Akbar. Our voices would become loud, so the Noble Prophet (peace and blessings be upon him) said: "O people! Do not exert yourselves so much, make it easy upon yourselves, for you are not calling upon one who is deaf or absent. Indeed, He hears, He is near." (One should also say Allahu Akbar while ascending stairs.)