I say, and with God's success: Whoever sleeps while standing, bowing, sitting, or prostrating, his ablution is not invalidated; because in sleeping in these positions, relaxation does not reach its limit. Likewise, if one sleeps cross-legged or in a sitting position. Ibn Abbas  reported: "He saw the Prophet  sleeping while prostrating until he snored or breathed heavily, then he stood up to pray. I said, O Messenger of God, you have slept. He said: Ablution is only required for one who sleeps lying down, for when one lies down, his joints relax." This is found in Sunan al-Tirmidhi 1: 111, Sunan Abu Dawood 1: 52, Sunan al-Daraqutni 1: 159, Musnad Abu Ya'la 4: 477, Musnad Abd ibn Hamid 1: 220, and Al-Mu'jam al-Kabir 12: 157. Ibn al-Mulaqqin said in Al-Khalasah 1: 53: It is weak. In Majma' al-Zawa'id, its narrators are trustworthy. See: I'la al-Sunan 1: 129. And from Abu Huraira , he said: "There is no ablution required for the sleeping person who is in a sitting position, nor for the standing sleeper, nor for the prostrating sleeper until he lies down. If he lies down, he should perform ablution," found in Sunan al-Bayhaqi al-Kabir 1: 122. Ibn Hajar said in Al-Talkhis 1: 120: Its chain is good, and it is a suspended narration. And from Amr al-Shu'ayb from his father from his grandfather, he said : "There is no ablution required for one who sleeps sitting until he lays his side on the ground," found in Al-Kamil 6: 467. Al-Qari said in Fath Bab al-Niqayah 1: 66: These hadiths, although individually they are not free from weakness, when they support each other, they do not drop below the level of good, and there is no explicit contradiction to them, so it is permissible to act upon them. See: Umdat al-Ri'ayah 1: 76, and Tabyin al-Haqaiq 1: 10, and Majma' al-Anhar 1: 20, and Al-Ikhtiyar 1: 15, and God knows best.