It came to pass on the next day that an evil spirit from God rushed upon Saul, and he prophesied in the midst of the house. David was playing the harp with his hand as he did day by day. Saul had his spear in his hand
“on the next day.” The day after Saul was angry about what the women sang.
“the house.” In this context, the “house” is the palace. There are a number of verses in the Bible where the palace is called the king’s “house.”