Is it required to rub between the toes every time one performs ablution (wudu’), or is it sufficient to do it once for each foot that is washed three times?

The obligatory act in ablution (wudu') is to wash the limbs once, ensuring that water reaches them. If water does not reach them except by rubbing (dalk), then rubbing becomes obligatory. Otherwise, rubbing is sunnah (recommended). It is obligatory to get water between the fingers and toes at least once. Scholars have agreed that what is obligatory in washing is the flowing of water over the limbs, and rubbing is not required unless water does not reach without it. Intertwining the fingers (takhleel al-asabi') is sunnah according to the majority of scholars, unless water does not reach between them except by intertwining with the hand, in which case it becomes fard (obligatory).