Grading: This hadith is sahih, and its chain is hasan on account of 'Uthman bin Muslim bin Hurmuz (who is also called 'Uthman bin 'Abdullah bin Hurmuz).
Technical note / Defect ('illah): Al-Mas'udi ('Abd al-Rahman bin 'Abdullah bin 'Utbah), Mis'ar bin Kidam and Hajjaj bin Artah narrated from him, as al-Daraqutni indicated in "al-'Ilal" (314), and Ibn Hibban mentioned him in "al-Thiqat".
Corroborating chains and supporting reports: 'Abd al-Malik bin 'Umayr corroborated him (mutaba'ah) in this hadith, and it is also narrated from 'Ali (may Allah be pleased with him) via other chains. The narrator al-Husayn bin Humayd (Ibn al-Rabi') has some weakness (lin), but he too has been corroborated.

Reference / Source: Al-Tirmidhi (3637) recorded it via Muhammad bin Isma'il al-Bukhari from Abu Nu'aym with this same chain, and al-Tirmidhi declared it "a sahih hadith".

Reference / Source: Ahmad recorded it in "al-Musnad" 2/ (744, 746, 1053), and al-Tirmidhi (after 3637), via Waki' bin al-Jarrah, from al-Mas'udi, from 'Uthman bin 'Abdullah bin Hurmuz, with this chain.
Note / Clarification: In this chain his name is given as "Ibn 'Abdullah".

Reference / Source: Ahmad (744) recorded it via Mis'ar bin Kidam from 'Uthman bin 'Abdullah bin Hurmuz; here too the name is "Ibn 'Abdullah".
Technical note / Defect ('illah): In another narration, in 'Umar bin Shabbah's "Tarikh al-Madinah" 2/602, his name is written as "'Uthman bin Salamah bin Hurmuz", which is probably a corruption (tahrif, a scribal error) of "Ibn Muslim".

Technical note / Defect ('illah): 'Abdullah bin Ahmad, in his additions to "al-Musnad" (947), narrated it via Hajjaj bin Artah as "from 'Uthman, from Abu 'Abdullah al-Makki". Al-Daraqutni clarified in "al-'Ilal" (314) that the kunyah of 'Uthman bin Muslim bin Hurmuz is itself "Abu 'Abdullah", so the correct chain is "from 'Uthman Abu 'Abdullah al-Makki"; that is, the word "from" ('an) between 'Uthman and Abu 'Abdullah is superfluous and should have been dropped.
Reference / Source: Al-Hafiz Ibn Hajar stated this very point explicitly in "Ta'jil al-Manfa'ah" in the biography of Abu 'Abdullah al-Makki.

Grading: By both of these routes the chain is hasan.
Reference / Source: 'Abdullah bin Ahmad (944) and Ibn Hibban (6311) recorded it via various routes from Sharik bin 'Abdullah al-Nakha'i, from 'Abd al-Malik bin 'Umayr. 'Abdullah bin Ahmad (946) also transmitted it via Salih bin Su'ayd (or Sa'id); both of them ('Abd al-Malik and Salih) narrate it from Nafi' bin Jubayr, from 'Ali bin Abi Talib (may Allah be pleased with him).

Reference / Source: Ahmad (1122) recorded it via Aswad bin 'Amir, with the chain "Nafi' bin Jubayr, from his father (Jubayr bin Mut'im), from 'Ali"; that is, it adds Jubayr bin Mut'im (may Allah be pleased with him).
Technical note / Defect ('illah): Al-Daraqutni said in "al-'Ilal" (314) that the correct version is that of those who narrated it as "Nafi' bin Jubayr, from 'Ali" without mentioning Jubayr (bin Mut'im) in it; Allah knows best.

Grading: Its chain is also hasan.
Reference / Source: Ahmad recorded it at (684 and 796) via Muhammad bin 'Ali (known as Ibn al-Hanafiyyah), from his father 'Ali bin Abi Talib (may Allah be pleased with him).

Grading: This chain is weak.
Technical note / Defect ('illah): Ahmad (1053) recorded it via Mujamma' bin Yahya, from 'Abdullah bin 'Imran, from 'Ali; this 'Abdullah bin 'Imran is "majhul" (unknown), and according to Ibn Sa'd's "al-Tabaqat" 1/353 a number of people narrated it from Mujamma' as "from 'Abdullah bin 'Imran, from a man (an unnamed person), from 'Ali", so this chain contains an unknown narrator and an unnamed one. 'Abdullah bin Ahmad (1300) recorded it via two routes from Nuh bin Qays, from Khalid bin Khalid, from Yusuf bin Mazin, from a man, from 'Ali; one of the two routes does not mention the unnamed man, and the correct version mentions him. Its chain is weak because Khalid bin Khalid is unknown and the Successor (tabi'i) is unnamed.

Grading: Its chain is not connected (muttasil).
Technical note / Defect ('illah): Al-Tirmidhi (3638) recorded it via Ibrahim bin Muhammad bin 'Ali from his grandfather, although he did not meet his grandfather (hearing from him is not established). Moreover, the narrator who transmits from Ibrahim is not solid (matin).

Grading: Its sixth route is also hasan.
Reference / Source: It was recorded by Ibn Sa'd 1/354, Ya'qub bin Shaybah in "al-Musnad", Ya'qub bin Sufyan in "al-Tarikh" and Qasim bin Thabit in "al-Dala'il" (as cited in "Jami' al-Athar" 4/366), via 'Umar bin 'Ali bin Abi Talib from his father.

Note / Clarification: Regarding the manner of the Prophet's (peace and blessings be upon him) walking (his gait), see the narration of Anas (may Allah be pleased with him) coming at number (7943), and see its explanation there as well.

General principle: After this hadith, al-Tirmidhi quoted from al-Asma'i the lexical explanation of the words that occur in the narration of 'Ali (may Allah be pleased with him) regarding the attributes of the Prophet (peace and blessings be upon him).

Important point: The word "al-shathn" means that the fingers and toes of the hands and feet are fleshy and sturdy (thick).

Important point: "Al-masrubah" means the fine line of hair from the chest to the navel which is like a long branch or rod.

Important point: "Al-sabab" means a slope, or descending from a height.

Note / Clarification: "Al-karadis" means the joints of the bones where two large bones meet; what is meant is that his (peace and blessings be upon him) limbs (joints) were large and sturdy.

Important point: "Dakhm al-lihyah" means that his (peace and blessings be upon him) blessed beard was thick, as is stated explicitly in the narration of Ibn al-Hanafiyyah from 'Ali (may Allah be pleased with him).