I say, and with God's success: The large stagnant water: which is that which does not move one of its ends by the movement of the other, and the scholars defined it by area, estimating it at ten cubits by ten cubits - that is, what equals (25) square meters of water surface area, and the depth from which the ground does not appear when scooping from it - it does not become impure except if one sees the trace of impurity in it by a change in its taste, color, or smell, even at the place of occurrence, even if the impurity has a substance, such as being visible and apparent, then one does not perform ablution from its place. Refer to: Umdat al-Ri'ayah 1: 88, and God knows best.