“Safe and sound” was originally applied to a sea vessel that had weathered a storm and was now safe in port, or at least in calmer seas; and sound in that it had suffered no damage in ancient times.
The phrase occurs in the New Testament, describing the way the Prodigal Son’s father receives the Prodigal back to the family. The celebration was said to have occurred because the father had received the son back “safe and sound”. This would have been the translation of the Greek text by the King James translators of 1611
27 And he said unto him, Thy brother is come; and thy father hath killed the fatted calf, because he hath received him safe and sound.