Narrated Abu Huraira: The Prophet said, "Allah created Adam in His picture, sixty cubits (about 30 meters) in height. When He created him, He said (to him), "Go and greet that group of angels sitting there, and listen what they will say in reply to you, for that will be your greeting and the greeting of your offspring." Adam (went and) said, 'As−Salamu alaikum (Peace be upon you).' They replied, 'AsSalamu−'Alaika wa Rahmatullah (Peace and Allah's Mercy be on you) So they increased 'Wa Rahmatullah' The Prophet added 'So whoever will enter Paradise, will be of the shape and picture of Adam Since then the creation of Adam's (offspring) (i.e. stature of human beings is being diminished continuously) to the present time."

Sahih al-Bukhari Vol 8, Book 8, Hadeeth No 246

Narrated `Abdullah bin `Amr: A man asked the Prophet , "What sort of deeds or (what qualities of) Islam are good?" The Prophet replied, 'To feed (the poor) and greet those whom you know and those whom you do not Know (See Hadith No. 27).

                                                          Sahih al-Bukhari Vol 1, Book 2, Hadeeth No 11