Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) said: The Noble Prophet (peace and blessings of Allah be upon him) said: "Take Ma'iz bin Malik and stone him to death." So we took him to Baqi' al-Gharqad, and by Allah, we neither tied him nor dug a pit; he simply stood, and we killed him by throwing bones, pieces of pottery, and stones at him.
Brief Explanation
(Commentary on Hadith 2355)
It is not necessary, according to anyone, to tie up (the person) at the time of stoning (rajm). There is a difference of opinion regarding digging a pit. According to Imam Malik, Abu Hanifah, and Ahmad rahimahumullah, a pit should not be dug for either a man or a woman. According to Qatadah, Abu Thawr, and Abu Yusuf, a pit should be dug for both; the evidence for this will be mentioned ahead. And according to Imam Malik rahimahullah, if the stoning is established by testimony, then a pit should be dug, but if it is established by confession, then it should not be dug. According to the Shafi‘is, a pit should not be dug for a man, but regarding a woman, there are three opinions: first, that it is recommended (mustahabb) to dig a pit up to her chest so that her private parts (‘awrah) are not exposed; second, that it is neither recommended nor disliked (makruh), rather it depends on the discretion of the ruler (hakim); third, that in the case of testimony, it is recommended so that she does not get an opportunity to escape (Nawawi, summarized).
This hadith supports the first opinion, that a pit should not be dug for anyone. Also, it indicates that a man should be stoned while standing, and a woman should be stoned while sitting, so that her modesty is not compromised.
And Allah knows best.