Musar do Koheleta 8:8

The Zohar writes (Parashas Vayechi 217b): When the time approaches for a person to depart from this world, it [the time of his departure] is announced, thirty days beforehand, in Gan Eden. It was taught: During these thirty days his soul departs every night and sees its place in the other world, although the person himself is unaware of this. Moreover, during these thirty days he no longer has dominion over his soul as he did previously, as it is written, “A man cannot rule over the spirit, etc.” (Koheles 8:8). Rabbi Yehudah said: Once these thirty days begin a man’s visage darkens and his form can no longer be seen on earth.