Is it permissible to use only the right hand to wash the face during ablution (Wudu')?

The fundamental principle is to use both hands when washing the face, following the practice of the Prophet, peace and blessings be upon him, and to ensure thoroughness. However, there is no harm in using one hand, whether the right or the left, to wash the face if it achieves full coverage with water, such as when the person performing ablution takes two or three scoops.