It was recorded by Abu Dawud (1/156), al-Tirmidhi (2/84–85), al-Hakim (1/267), and—citing him—al-Bayhaqi (2/146), through the chain of Muhammad b. Ishaq → Abd al-Rahman b. al-Aswad → his father → Ibn Masud. Al-Tirmidhi graded it “hasan gharib,” while al-Hakim ruled it “sahih according to Muslim’s conditions,” and al-Dhahabi followed him—so they both said. Al-Hakim (1/230), and in turn al-Bayhaqi, also brought it by another route: al-Alaʾ b. Abd al-Jabbar al-Attar → Abd al-Wahid b. Ziyad → al-Hasan b. Ubayd Allah → Abd al-Rahman b. al-Aswad, with the same wording. He labeled it “sahih on the conditions of both Shaykhs,” and al-Dhahabi concurred. That verdict is inaccurate, for al-Hasan b. Ubayd Allah al-Nakhai is not one of al-Bukhari’s narrators, and al-Alaʾ b. Abd al-Jabbar al-Attar is not among Muslim’s. The hadith is therefore merely sound (sahih); its transmitters, however, are of the caliber found in the two Sahihs. Al-Tirmidhi adds, “The scholars act upon it.” Al-Nawawi (3/463) notes: “The scholars unanimously agree that both tashahhuds are to be recited silently and that raising the voice is disliked, and they adduce this hadith of Ibn Masud as proof.”