Shaykh Adil Murshid et al.
(1) إسناده صحيح، المسعُودي - وهو عبد الرحمن بن عبد الله بن عُتبة - وإن كان تغيّر حفظُه، فسماعُ جعفر بن عون منه قديمٌ.
Grading: Its chain is sahih.
Technical note: Although al-Mas'udi (Abd al-Rahman bin Abdullah bin 'Utbah) suffered a deterioration of memory late in life, Ja'far bin 'Awn heard from him early (before the deterioration).
وأخرجه البيهقي في "المدخل إلى السنن الكبرى" (99)، ومن طريقه ابن عساكر في "تاريخ دمشق" 33/ 120 عن أبي عبد الله الحاكم، بهذا الإسناد.
Reference / Source: It was recorded by al-Bayhaqi in "al-Madkhal ila al-Sunan al-Kubra" (99), and through him by Ibn 'Asakir in "Tarikh Dimashq" 33/ 120, from Abu Abdullah al-Hakim with this same chain.
وأخرج مسلم (800) (248) من طريق معن بن عبد الرحمن بن عبد الله بن مسعود، عن جعفر بن عمرو بن حريث، عن أبيه، عن ابن مسعود قال: قال النبي ﷺ: "شهيدًا عليهم ما دمتُ فيهم، أو ما كنتُ فيهم".
Reference / Source: Imam Muslim (800) (248) recorded via Ma'n bin Abd al-Rahman bin Abdullah bin Mas'ud, from Ja'far bin 'Amr bin Hurayth, from his father, from Ibn Mas'ud, that the Prophet (peace and blessings be upon him) said: "I will be a witness over them as long as I remain among them" (or the wording is "as long as I was among them").
ويشهدُ للشطر الأول منه ما أخرجه أحمد (6/ 3606) و 7 / (4118)، والبخاري (4583) و (5049) و (5055)، ومسلم (800) (247)، وأبو داود (3668)، والترمذي (3025)، والنسائي (8021) و (8024) و (8025)، و (11039)، وابن حبان (735) من طريق عبيدة السَّلْماني، عن ابن مسعود نفسه.
Corroborating chains and supporting reports: A supporting report for the first part of the hadith is the narration recorded by Ahmad (6/ 3606, 7/ 4118), al-Bukhari (4583, 5049, 5055), Muslim (800) (247), Abu Dawud (3668), al-Tirmidhi (3025), al-Nasa'i (8021, 8024, 8025, 11039) and Ibn Hibban (735) via 'Abidah al-Salmani, from Ibn Mas'ud himself.
ولقوله ﷺ في آخر الحديث هنا: "رضيتُ لكم ما رضي لكم ابن أمّ عبدٍ" شاهدٌ من حديث ابن مسعود نفسه تقدَّم عند المصنف برقم (5456)، وإسناده صحيح كذلك.
Corroborating chains and supporting reports: And for the final statement of the Prophet (peace and blessings be upon him): "I am pleased for you with what Ibn Umm 'Abd (Abdullah bin Mas'ud) is pleased with for you", there is a supporting report in the hadith of Ibn Mas'ud himself, which has already passed with the author (al-Hakim) at number (5456), and its chain is also sahih.
وآخر من مرسل القاسم بن عبد الرحمن بن عبد الله بن مسعود تقدَّم برقم (5473) و (5474).
Corroborating chains and supporting reports: And another supporting report, from the "mursal" narration of al-Qasim bin Abd al-Rahman bin Abdullah bin Mas'ud, has already passed at numbers (5473) and (5474).
Source: Al-Mustadrak ala al-Sahihayn (Takhrij & Tahqiq: Shaykh Adil Murshid et al.), Page: 5480