From Sahih Bukhari (Hadith 3328):
Narrated Zainab bint Abi Salama:Um Salama said, "Um Sulaim said, 'O Allah's Messenger (ﷺ)! 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)?
Reference: Bukhari 3328