This chain is sound according to al-Bukhari’s standards. Ibn al-Qayyim, however, slipped in Zad al-Maʿad (1/85): after describing the Prophet’s iftirash between the two prostrations, he wrote, “No other sitting posture at this point has been recorded from him.” He apparently did not have Ibn ʿAbbas’s report in view when he wrote that; otherwise, the hadith is unquestionably authentic and probative, and more than one of the early righteous scholars acted upon it. Al-Tirmidhi remarks: “Some scholars among the Companions of the Prophet have adopted this hadith and see no objection to iqʿa; it is also the view of a number of Meccan jurists and scholars.” He then adds, “Most scholars, however, dislike iqʿa between the two prostrations.” I say: Those who censure it base themselves on reports that prohibit iqʿa. Most of them were transmitted by al-Bayhaqi (2/120); all are weak, as al-Nawawi states in his commentary on Muslim, and al-Shawkani details their defects in Nayl al-Awtar (2/232)—save for two hadiths he left unchallenged. Concerning the first he judged it hasan: the report of Abu Hurayrah, “The Messenger of Allah forbade me three things: pecking like a rooster, iqʿa like a dog, and turning one’s head like a fox.” The second is the hadith of Samurah b. Jundub: “The Messenger of Allah forbade iqʿa in the prayer.” Both require closer scrutiny.