The Prophet ﷺ 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.  

عَنِ النَّبِيِّ ﷺ قَالَ خَلَقَ اللَّهُ آدَمَ وَطُولُهُ سِتُّونَ ذِرَاعًا ثُمَّ قَالَ اذْهَبْ فَسَلِّمْ عَلَى أُولَئِكَ مِنَ الْمَلاَئِكَةِ فَاسْتَمِعْ مَا يُحَيُّونَكَ 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 حَتَّى الآنَ