Ṣaḥīḥ and ḥasan aḥādīth are accepted. This includes aḥādīth which are ṣaḥīḥ li dhātihī, ṣaḥīḥ li ghayrihī, ḥasan li dhātihī and ḥasan li ghayrihī.
However, even though the narrations may be accepted, it does not necessarily mean that the ḥadīth will be acted upon. Such as the case when the narration may have been made mansūkh (abrogated) or may go against another ḥadīth.
For example:
حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، قَالَ حَدَّثَنَا سُفْيَانُ، {عَنْ عَمْرٍو،} قَالَ أَخْبَرَنِي أَبُو مَعْبَدٍ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ كُنْتُ أَعْرِفُ انْقِضَاءَ صَلاَةِ النَّبِيِّ صلى الله عليه وسلم بِالتَّكْبِيرِ.
Ibn ‘Abbās said: I used to recognise the completion of the prayer of the Prophet ﷺ by hearing takbīr.[1]
Imām Nawāwi narrates that: Ibn Baṭṭāl and others narrate that the different schools of thought, as well as others, agree that it is not recommended to raise the voice for takbīr at the end of ṣalāh. Thus, even though the ḥadīth above may be authentic, it is not necessarily acted upon.
As for ḍaīf aḥādīth, its ruling is that they are not accepted[2] except that they may be used for purposes of targhīb (encouragement) and tarhīb (disencouragement).
Conditions to accept a ḍaīf ḥadīth according to Ibn Ḥājar
Ibn Ḥājar, Sakhāwī and others have said there is a difference between ḍaīf shadīd (major weakness) and ḍaīf khafī (minor weakness).
Ibn Ḥājar mentions three situations when you can accept a ḍaīf narration. The narration should:
- not be ḍaīf shadīd;[3]
- conform with the principles of sharī’ah; and
- be acted upon with caution, as it may not be from the Prophet ﷺ.
[1] Ṣaḥīḥ Bukhāri 842
[2] Ḍaīf aḥādīth are accepted according to those who give preference to ḍaīf aḥādīth over qiyās, such as Imām Aḥmad, Abū Dawūd and others.
[3] For example it is narrated by a severe liar, or one who is accused of lying, or one who is reckless in their narrations