Correct sujood (prostration)
Question

We see some worshippers – may Allah guide us and them – when they do sujood, they tilt their foreheads up so that they hardly touch the ground. If we try to advise them, they come up with silly excuses (such as not wanting to spoil their headgear, etc). Is their prayer valid? What is your advice to them? May Allah reward you with good.
Praise be to Allah.When doing sujood, they must place their foreheads firmly on the ground, because Anas ibn Malik (may Allah be pleased with him) said: “We used to pray with the Prophet (peace and blessings of Allah be upon him) when it was very hot, and if one of us could not place his forehead firmly on the ground, he would spread his garment out and do sujood on it.” Simply touching the place of sujood lightly with one’s  forehead is not enough. Therefore their sujood is not correct, and their prayer is not valid, because sujood is one of the pillars (essential parts) of prayer.
And Allah knows best.