The Messenger of Allah ﷺ used to give the salam to his right and to his left until the whiteness of his cheek could be seen, saying, "As-salamu alaykum wa rahmatullah, as-salamu alaykum wa rahmatullah."
أن رسول الله ﷺ كان يسلم عن يمينه، وعن شماله، حتى يرى بياض خده السلام عليكم ورحمة الله، السلام عليكم ورحمة الله.
Reported by Abu Dawud (996), Tirmidhi (295), Nasai (1084, 1320), and Ibn Majah (914), all of them through chains from Abu Ishaq, from Abu Ahwas, from Abdullah bin Masud, who narrated something similar. The wording given is that of Abu Dawud. Tirmidhi said, "hasan sahih." However, Abu Dawud transmitted from Shubah that he used to deny that the hadith of Abu Ishaq was marfu.I say, Abu Ishaq is Subayi, a mudallis whose narrations became mixed up later in life, but some narrators transmitted from him before this mixing occurred, among them Sufyan Thawri. Abu Dawud himself cited many chains through Abu Ishaq, and for this reason Ibn Khuzayma (728) and Ibn Hibban (1990, 1993) graded it sahih after transmitting it through his route. Al-Hafiz quoted from Aqeeli, "The chains are sahih and established regarding the hadith of Ibn Masud on the two tasleems, but nothing is authentic regarding a single tasleem." Talkhis (1/270).So perhaps he did not practice tadlis in this hadith, and his mixing did not affect it here, since there are many other routes that do not include Abu Ishaq. Among them is what Abdul-Razzaq (3127) narrated from Mamar and Thawri, from Hammad, from Abu Duha, from Masruq, from Abdullah bin Masud, who said, "Among the things I have not forgotten from the Messenger of Allah ﷺ is that he used to say the tasleem to his right, 'Peace and the mercy of Allah be upon you,' until we could see the whiteness of his cheek, and to his left, 'Peace and the mercy of Allah be upon you,' until we could see the whiteness of his cheek as well."Through Abdul-Razzaq's route, this was also narrated by Tabarani in al-Kabir (10177) and Imam Ahmad (3887), though in his version "Hammad" was corrupted to "Jabir." Its chain is sahih.Among these routes is also what Ibn Hibban (1994) and Bayhaqi (2/177) narrated, both through Zakariya (who is Ibn Abu Zaida), from Shaybi, from Masruq, with a similar wording.