Peace be upon you,
There are many hadiths which order women not to refuse sex with their husbands. Some of which I know:
1) Prophet Muhammad has siad: "When a man calls his wife for sexual intimacy, then she should come, even if she is (busy) in the cooking area.” (Sunan al-Tirmizi & Sunan al-Nasa’i)
2) The Messenger of Allaah (peace and blessings of Allaah be upon him) said: ‘If a man calls his wife to his bed and she refuses [and does not come], and he spends the night angry with her, the angels will curse her until morning." (Reported by al-Bukhaari)
3) Holy Prophet (S.A.W) said: By the One in Whose hand is my soul, there is no man who calls his wife to his bed and she refuses, but the One Who is above the heavens [i.e. Allaah] will be angry with her, until he (her husband) is pleased with her.”
Therefore, I encourage women not to refuse what their husbands say. Because it is a sin for a woman to make her husband angry, when he commands (but must refuse which is forbidden).