If a person in wudu breaks his wudu to open the door, does he repeat the wudu or resume it?

Question:
May Allah bless you. The questioner is your sister, Umm Muhammad, residing in al-Bahah, the Kingdom of Saudi Arabia. In her first question, she says: If I am in a state of wudu and only my feet remain to be washed, and the door is knocked on—whether by my husband or one of my children—and I go to open the door, am I required to repeat the wudu from the beginning when I return, or do I only wash the remaining feet?

Answer:
If you return in a short time that does not take long, you wash only the feet and build upon what you washed from the beginning of the wudu, because the continuity (muwalah) has not been broken. However, if the time is long and you do not return until after a period, it is necessary to repeat the wudu from the beginning because the continuity has been broken. The criterion, as the scholars say, is that one does not delay washing a limb until the one before it dries or becomes dry in moderate weather. So, if you return in a short time such that the washed limb has not dried, you continue the wudu and complete it. But if the limbs have dried due to the length of time, it is necessary to repeat the wudu from the beginning because the continuity has been broken. Yes.