Narrated Abu Huraira:

The Prophet ﷺ said, "Allah created Adam in his complete shape and form (directly), 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 form of Adam. Since then the creation of Adam's (offspring) (i.e. stature of human beings is being diminished continuously) to the present time."

حَدَّثَنَا يَحْيَى بْنُ جَعْفَرٍ، حَدَّثَنَا عَبْدُ الرَّزَّاقِ، عَنْ مَعْمَرٍ، عَنْ هَمَّامٍ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ ﷺ قَالَ
" خَلَقَ اللَّهُ آدَمَ عَلَى صُورَتِهِ، طُولُهُ سِتُّونَ ذِرَاعًا، فَلَمَّا خَلَقَهُ قَالَ اذْهَبْ فَسَلِّمْ عَلَى أُولَئِكَ النَّفَرِ مِنَ الْمَلاَئِكَةِ جُلُوسٌ، فَاسْتَمِعْ مَا يُحَيُّونَكَ، فَإِنَّهَا تَحِيَّتُكَ وَتَحِيَّةُ ذُرِّيَّتِكَ. فَقَالَ السَّلاَمُ عَلَيْكُمْ. فَقَالُوا السَّلاَمُ عَلَيْكَ وَرَحْمَةُ اللَّهِ. فَزَادُوهُ وَرَحْمَةُ اللَّهِ، فَكُلُّ مَنْ يَدْخُلُ الْجَنَّةَ عَلَى صُورَةِ آدَمَ، فَلَمْ يَزَلِ الْخَلْقُ يَنْقُصُ بَعْدُ حَتَّى الآنَ ".