The Śūraṅgama Sūtra: Volume X - The Delusions of the Five Skandhas

Your body initially comes into being due to the mental conception of your parents. If your mind lacked conception, you would not be drawn to them and could not enter your parents' realm of desire to perpetuate your life. In the intermediate state, sentient beings encounter their parents and take rebirth because the mental faculty conceives the idea of seeking rebirth and acquiring a physical form. As I previously stated: if one mentally contemplates the taste of vinegar, saliva arises in the mouth; if one mentally envisions standing atop a high mountain, a tingling sensation arises in the soles of the feet. Yet no actual precipice exists before you, nor has any sour substance materialized. Your physical body certainly has not made contact with any object conjured by your imagination. How then does saliva flow merely from discussing the taste of vinegar? Therefore, you should understand that your presently manifested physical form is called the fundamental solidified delusion. This indicates that the aggregate of form is a solidified delusion.