Srimad Bhagavatam Canto 04, Chapter 29, Text 67

 SB 4.29.67

adrstam asrutam catra
 kvacin manasi drsyate
yatha tathanumantavyam
 desa-kala-kriyasrayam
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
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.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
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.
Srimad Bhagavatam Canto 04, Chapter 29, Text 66
Srimad Bhagavatam Canto 04, Chapter 29, Text 68