Eccl 2:18-23 –
Yea, I hated all my labour which I had taken under the sun: because I should leave it unto the man that shall be after me. And who knoweth whether he shall be a wise man or a fool? yet shall he have rule over all my labour wherein I have laboured, and wherein I have shewed myself wise under the sun. This is also vanity.
Therefore I went about to cause my heart to despair of all the labour which I took under the sun. For there is a man whose labour is in wisdom, and in knowledge, and in equity; yet to a man that hath not laboured therein shall he leave it for his portion. This also is vanity and a great evil.
For what hath man of all his labour, and of the vexation of his heart, wherein he hath laboured under the sun? For all his days are sorrows, and his travail grief; yea, his heart taketh not rest in the night. This is also vanity.
For the SIH devotional on this subject: