First of all, we’d like to state that in Islam, purification is of high esteem to the extent that the Prophet (peace and blessings be upon him) regarded it as a half of one’s iman (faith), saying, “Purification is half of the faith.”

Islam is a religion that pays attention to the cleanliness, decency, and the good appearance and smell of its adherents. Muslims are recommended to appear decent and clean.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: Parents don’t necessarily need to wash the duvet, bed sheets, and pillow cases following conjugal relations with your spouse unless, of course, you are certain that semen has fallen on them and you are using the same for Prayer, in which case you need to wash the same or at least the spot of semen that has come in contact with. Should it be dry, however, it can be scraped off, though washing it is preferred.

If, on the other hand, you don’t suspect that semen has fallen on the duvet or bed sheets, then you need not worry. For according to the principles of jurisprudence, we are to assume that things are pure unless proven otherwise.
Having said this, however, I must point out the following: It is generally assumed that the married couple engaging in sexual intercourse make use of some piece of cloth or tissues to wipe their genitals clean following the act. Otherwise, it is more than likely that semen drops may fall on the bed sheets, in which case one must wash them before using the same for Prayers.