I say, and with God's success: It is purified by drying in the sun and wind; because it is connected to the ground, it takes its ruling; as Abu Qilabah said: "The dryness of the earth is its purification." And as narrated by Abu Dawood in his Sunan from Nafi', he said: "Ibn Umar was asked about walls that contain excrement and urine of people and the dung of animals, he said: If rain falls on them and the winds dry them, there is no harm in praying in them." Refer to: Al-Bahr Al-Ra'iq 1: 237, Al-Wiqayah p. 131, and the explanation of Al-Wiqayah by Ibn Malak Q19/B, and God knows best.