Cosmas of Prague wrote in Latin in his Chronica Boëmorum ("Chronicle of Bohemians") that Bolesław was born three days before the death of Judith, who died in VIII Calends of January (25 December) of 1085.
Cosmas dari Praha menulis dengan bahasa Latin di dalam Chronica Boëmorum ("Chronicle of Bohemians") bahwa Bolesław lahir tiga hari sebelum kematian Judith, yang meninggal pada VIII Kalends Januari (25 Desember) tahun 1085.