It is also recorded by al-Bukhārī (2/21) and Muslim (4/1882/57), through another chain from Abū Hurayrah, but it does not contain the passage relevant here. It is further supported by:

Fifth: A man from Banū Sulayṭ reported that he passed by the Prophet, who was seated at the door of his mosque with his knees drawn up, wearing a qitr garment.... It was recorded by Aḥmad (4/69; 5/24, 381). I say: Its chain of transmission is authentic.

Sixth: Ḥanash ibn al-Muʿtamir narrated from ʿAlī that ʿAlī was in Yemen, where they dug a pit for a lion. Then a man came and fell into it, catching hold of another ... [the hadith]. He said: They brought the matter before the Prophet, who had been reclining; then he drew up his knees....

It was narrated by Aḥmad (1/152), and its chain is good.

Seventh: In the hadith of al-Tanūkhī, Heraclius’s envoy to the Prophet, he said: “I set out with his letter until I came to Tabūk, where I found him sitting among his Companions with his knees drawn up....” It was recorded by Aḥmad (3/441–442), and its chain is good as corroborative evidence.

In sum, the hadith is authentic. It does no harm that its narrator is accused, for even a liar may speak the truth; and what evidence of his truthfulness here could be greater than these supporting reports?