I say, and with God's success: It is to wash them in succession so that the first limb does not dry before the second limb is washed, provided the air is moderate, by gathering the parts of ablution in one place for washing, and not engaging in another action during the ablution that would cause some parts of the ablution to dry. However, if the face or hand is dried with a towel before washing the foot, the continuity is not broken, and observing this is a Sunnah for us and not a condition, so that if the succession is interrupted, his ablution is still valid according to us. Refer to: The Noble Discourse Regarding the Towel by Imam al-Laknawi, edited by Dr. Salah Abu al-Hajj, p. 23, and God knows best.