import arcpy, os

input_fgdb = r'C:Somedatabase.gdb'
output_fgdb = r'C:Someoutputdatabase.gdb'

arcpy.env.workspace = input_fgdb
rasterlist = [r for r in arcpy.ListRasters() if 'day' in r]

for r in rasterlist:
    arcpy.CopyRaster_management(in_raster=r, out_rasterdataset=os.path.join(output_fgdb,r))