كانت لي ساعة من السحر أدخل فيها على رسول الله صلى الله عليه وسلم، فإن كان قائما يصلي سبح بي، فكان ذاك إذنه لي، وإن لم يكن يصلي أذن لي.
(‘Ali said) There was a certain time in which I would enter in the presence of the Messenger of Allah salla Llahu ‘alayhi wa sallam. If he was reading salah, he would make tasbih for me; this was his way of granting me permission (to enter). If he was not reading salah, he would permit me (to enter).
This hadith is narrated by ‘Ali and Abu Umamah radiya Llahu ‘anhuma.
Imam Ahmed, Ibn Khuzaimah and others narrate from al Harith ibn Yazid al ‘Ukli — from Abu Zur’ah — from ‘Abdullah ibn Nujayy who said, “‘Ali said…”
There is a difference of opinion regarding the narrator ‘Abdullah ibn Nujayy. Yahya ibn Ma’in said, “He did not hear (hadith) from ‘Ali.” Al Bazzar, on the other hand, established that he did in fact hear from ‘Ali. However, Ibn Ma’in is more knowledgeable.
As I explained in the original work, there is a difference of opinion regarding the grading of this hadith. Ibn al Sakan authenticated the hadith.
Imam al Nawawi writes, “This hadith is da’if (weak) and mudtarib (inconsistent and unresolvably problematic). The narrator of this hadith, ‘Abdullah ibn Nujayy is da’if (weak). There are other similar statements from al Bayhaqi and Ibn Hajar.
Imam Ahmed and al Bazzar narrate from Yahya ibn Ayub — from ‘Ubaidullah ibn Zahr — from ‘Ali ibn Yazid — from al Qasim — from Abu Umamah who said that ‘Ali ibn Abi Talib radiya Llahu ‘anhu informed him that he used to go to Nabi salla Llahu ‘alayhi wa sallam. He said, “When I found him salla Llahu ‘alayhi wa sallam reading salah he would make tasbih and I would enter. If he wasn’t reading salah, he would (simply) grant me permission.”
There is a difference of opinion regarding the status of ‘Ubaidullah ibn Zahr al Damri. However, most agree he is da’if (weak). In fact, Ibn Hibban says, “He is an extreme munkar of hadith (a weak transmitter that narrates something which contradicts another authentic hadith). He narrates fabrications from reliable narrators. He brings forth disastrous narrations when transmitting from ‘Ali ibn Yazid. If ‘Ubaidullah ibn Zahr, ‘Ali ibn Yazid, and al Qasim Abu ‘Abdul Rahman are found in one chain of transmission, the matn (text) was simply fabricated by them. Therefore, it is not permissible to use this as a proof. In fact, it is better to steer completely away, in these conditions, from the narration of ‘Ubaidullah ibn Zahr.”
As you can see, the hadith is narrated by the same people that Ibn Hibban mentioned.
In short, the hadith is da’if (weak) because the chain of transmission from ‘Ali is inconsistent and unresolvably problematic (mudtarab). The chain of transmission contains the narrator Ibn Nujayy, whom there is a difference of opinion regarding. The chain of transmission from Abu Umamah contains the narrator ‘Ubaidullah ibn Zahr. Ibn Hibban’s statements regarding him have already been mentioned.
 Imam Ahmed: Musnad Ahmed, 1/77; Ibn Khuzaimah: Sahih ibn Khuzaimah, 2/902.
 Ibn Hajar: al Talkhis al Habir, 1/283.
 Imam al Nawawi: Khulasat al Ahkam, 1/499.
 Imam al Bayhaqi: al Sunan al Kubra, 2/247; ibn Hajar: Talkhis al Habir, 1/283.
 Imam Ahmed: Musnad Ahmed, 1/112; al Bazzar: Musnad al Bazzar, hadith no. 498.
 Ibn Hibban: Kitab al Majruhin, 2/62-63.