SB 4.29.67

अदृष्टमश्रुतं चात्र क्वचिन्मनसि दृश्यते ।
यथा तथानुमन्तव्यं देशकालक्रियाश्रयम् ॥६७॥

adṛṣṭam aśrutaṁ cātra
kvacin manasi dṛśyate
yathā tathānumantavyaṁ
deśa-kāla-kriyāśrayam

adṛṣṭam—never experienced; aśrutam—never heard; ca—and; atra—in this life; kvacit—at some time; manasi—in the mind; dṛśyate—is visible; yathā—as; tathā—accordingly; anumantavyam—to be understood; deśa—place; kāla—time; kriyā—activity; āśrayam—depending on.

Sometimes in a dream we see something never experienced or heard of in this life, but all these incidents have been experienced at different times, in different places and in different conditions.

In the previous verse it was explained that in dreams we see that which was experienced during the day. But why is it that we sometimes in our dreams see what we have never heard of or seen at any time during this life? Here it is stated that even though such events may not be experienced in this life, they were experienced in previous lives. According to time and circumstance, they combine so that in dreams we see something wonderful that we have never experienced. For instance, we may see an ocean on the peak of a mountain. Or we may see that the ocean has dried up. These are simply combinations of different experiences in time and space. Sometimes we may see a golden mountain, and this is due to our having experienced gold and mountains separately. In the dream, under illusion, we combine these separate factors. In this way we are able to see golden mountains, or stars during the day. The conclusion is that these are all mental concoctions, although they have actually been experienced in different circumstances. They have simply combined together in a dream. This fact is further explained in the following verse.