Source: Ṣaḥīḥ Muslim 2564
The beauty that one achieves by outer adornments and clothes is bound to vanish. If a man thinks that he is wealthy, wears good clothes and looks pleasing, all this will increase his value in peoples eyes for a short time because the outer beauty is bound to vanish. Nothing in this world is permanent. These temporary worldly materials end and hence the value of a man is lost with them!
But if one focuses on the inner beauty, the beauty of heart and soul than that will stay with him if all else fails. It is the beauty of heart and soul that gives value to man in peoples eyes and most importantly, in Allah's eyes. The inner beauty can be seen in one's character, morals, love, ethics, knowledge, and attitude. This beauty increases as we grow old.
In the eyes of Allah, the outer beauty is of such little importance, its the heart that matters. If a person is wealthy with good looks and an ill heart than he is Nothing in front of Allah but if a person has nothing but has a good and sound heart that he is loved more by Allah. Allah looks at our intentions, our thoughts not our clothes and wealth.
However, this doesn't mean that one should not care about how he looks. It is important. As a matter of fact, in Islam, we are required to look good and modest but not at the cost of the state of our heart. Also, the condition of our heart is much preferred and it is this condition that will take us to hell or heaven. Our outer condition is meant for this Duniya but the condition of our heart is what is important in the hereafter.
To sum up, we can say that man should not be engaged in outer beauty very much; he should give importance to inner beauty, and he should want the maturity that will last throughout life.
May Allah guide us all.