Narrated Abu Huraira: The Prophet said, "Allah created Adam, making him 60 cubits tall. When He created him, He said to him, "Go and greet that group of angels, and listen to their reply, for it will be your greeting (salutation) and the greeting (salutations of your offspring." So, Adam said (to the angels), As-Salamu Alaikum (i.e. Peace be upon you). The angels said, "As-salamu Alaika wa Rahmatu-l-lahi" (i.e. Peace and Allah's Mercy be upon you). Thus the angels added to Adam's salutation the expression, 'Wa Rahmatu-l-lahi,' Any person who will enter Paradise will resemble Adam (in appearance and figure). People have been decreasing in stature since Adam's creation. (Translation of Sahih Bukhari, Volume 4, Book 55, Number 543)"
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: "Allah, the Exalted and Glorious, created Adam in His own image with His length of sixty cubits, and as He created him He told him to greet that group, and that was a party of angels sitting there, and listen to the response that they give him, for it would form his greeting and that of his offspring. He then went away and said: Peace be upon you! They (the angels) said: May there be peace upon you and the Mercy of Allah, and they made an addition of" Mercy of Allah". So he who would get into Paradise would get in the form of Adam, his length being sixty cubits, then the people who followed him continued to diminish in size up to this day. (Translation of Sahih Muslim, Book 040, Number 6809)"