No source for ceiling leak?

Last friday AM I found a big pool of water in our basement; coming from the ceiling where there are no water pipes in the area. I pulled out a few of the water logged ceiling tiles and the wood beams were soaked. We checked both 1st and 2nd floor bathrooms but saw nothing. Turned off the water at the main pipe. We headed out of town for a pre arranged trip.We were thinking the water was following a beam or board down. Our daughter checked the basement the next day no water anywhere. On Sunday pm we returned and turned the water back on. no leak. checked during the night, no leak. Since then no water leaking. The soil level is lower then the ceiling so not from the outside. We are just waiting for the return altho we have not flushed the 2nd floor toilet. All we could imagine was tearing out walls and floors "looking" for a source. House was built in 1944.