Sahih Muslim Book 40, Hadith Number 6809.
Chapter : There would enter Paradise some people whose hearts would be like those of birds.
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.