“Falling down on the chin” phrase is denoting complete submission in humility and humbleness. It is further clarified in 17:109.
17:107 Say, 'Believe in it or do not believe in it.' Those who have been given knowledge before it, when it is recited to them, they fall down to their chins, prostrating.'
[Zaqan = Chin, and not face] See 17:109 below
17:108 They say, 'Glory be to our Lord. Surely, the promise of our Lord has been fulfilled.'
17:109 AND SO THEY FALL DOWN ON THEIR CHINS, WEEPING, AND INCREASING IN HUMILITY.
37:103 Falamma aslama watallahu LILJABEENI
Literal translation: Then when both of them had submitted and he put him down upon his FOREHEAD,
37:103 As both of them had surrendered themselves (to God), he made Ishmael further submit in gratitude. [Contrary to popular tradition, Abraham never envisioned or intended to slaughter his son. God does not play games with His servants. Literal 'forehead to ground' = complete submission in gratitude]