Sahih Bukhari
Prophets
Volume: 004 / Book Number: 055 / Hadith Number: 545
Narrated Abu Salama:
Um Salama said, "Um Salaim said, 'O Allah's Apostle! Allah does not refrain from saying the truth! Is it obligatory for a woman to take a bath after she gets nocturnal discharge?' He said, 'Yes, if she notices the water (i.e. discharge).' Um Salama smiled and said, 'Does a woman get discharge?' Allah's Apostle said. 'Then why does a child resemble (its mother)?"