al-Kashshi comments:
فدل هذا الحديث على منزلة الرجل من عقله و اهتمامه بأمر دينه إن شاء الله
This narration indicates the high station of the man in terms of his intellect and his scrupulousness in the matter of his religion, if Allah wills.
I say: Without a doubt Nasr must have been a very close companion of al-Sadiq to have been told the identity of the successor. This led him to avoid falling into error when the Fitna of the Fathiyya occurred.
Another narration in al-Kashshi has the same theme:
حدثني حمدويه قال: حدثني الحسين بن موسى، عن سليمان الصيدي، عن نصر بن قابوس قال: كنت عند أبي الحسن عليه السلام في منزله، فأخذ بيدي فوقفني على بيت من الدار، فدفع الباب فإذا علي عليه السلام ابنه، وفي يده كتاب ينظر إليه، فقال لي: يا نصر تعرف هذا؟ قلت: نعم هذا علي عليه السلام ابنك، قال: يا نصر، أتدري ما هذا الكتاب الذي ينظر فيه؟ فقلت: لا، قال: هذا الجفر الذي لا ينظر فيه إلا نبي أو وصي
قال الحسن بن موسى: فلعمري ما شك نصر فيه ولا ارتاب حتى أتاه وفاة أبي الحسن عليه السلام
Hamduwayh – al-Hasan b. Musa – Sulayman al-Saydi – Nasr b. Qabus who said: I was with Abi al-Hasan عليه السلام in his house when he took me by the hand and made me stand outside a room in the house, then he opened the door and there was Ali his son [inside] with a book in his hand which he was perusing. He [al-Kadhim] said to me: O Nasr – do you know this one? I said: Indeed, it is your son Ali. He said: O Nasr – do you know what that book which he is looking into is? I said: No, he said: that is the Jafr which no one can read except a prophet or a successor.
al-Hasan b. Musa [the sub-narrator] comments: By my life! Nasr never doubted concerning him [al-Ridha] nor did he waver until news about the death of Abi al-Hasan [al-Ridha] came to him i.e. he believed in the Imam all his life.
al-Najashi says about this Nasr b. Qabus:
روى عن أبي عبد الله وأبي إبراهيم وأبي الحسن الرضا عليهم السلام وكان ذا منزلة عندهم
He narrated from Abi Abdillah, Abu Ibrahim and Abi al-Hasan al-Ridha عليهم السلامand had a position of great merit in their eyes
al-Tusi says:
وروى أنه كان وكيلا لأبي عبد الله عليه السلام عشرين سنة ولم يعلم أنه وكيل وكان خيرا فاضلا
It is narrated that he [Nasr] was a Wakil of Abi Abdillah عليه السلام for a period of twenty years without it being known that he was a Wakil. He was both good and meritorious.