Hekayat 42 from Chapter 8 of Golestan of Saadi

Not everyone who is beautiful in appearance has a beautiful character. The matter lies within, not in the outward form.

You can recognize a man's outward qualities in a day,

Seeing the extent of his knowledge and skills,

But be wary and not deceived by his inner nature,

For the evil of the soul is not revealed in years.

نه هر که به صورت نکوست سیرت زیبا در اوست. کار اندرون دارد نه پوست.

توان شناخت به یک روز در شمایل مرد

که تا کجاش رسیده‌ست پایگاه علوم

ولی ز باطنش ایمن مباش و غره مشو

که خبث نفس نگردد به سالها معلوم