The muhaddithoon state that the saheeh hadeeth which is most likely attributable to the Prophet (peace and blessings of Allaah be upon him) is the hadeeth which fulfils all of the five following conditions:
1. Each of its narrators is of good character
2. Each of its narrators has a precise memory
3. The isnaad is uninterrupted from beginning to end
4. The hadeeth is sound and free of any shudhoodh (irregularity) in its isnaad or matn (text)
5. The hadeeth is sound and free of any ‘illah (fault) in its isnaad or text.
This has been discussed in the answer to question no. 79163.
The fourth and fifth conditions are among the most precise of conditions and the most difficult for the critic, because proving them required intense research and precision, bringing together all the isnaads and narrations of the hadeeth, as well as extensive experience in the sciences of hadeeth and specialization in criticism. Hence many of the later muhadditheen chose to err on the side of caution in their verdicts, and they limited their studies to checking the outward appearance of the isnaad to check whether it met the first three conditions, so if a specific isnaad met these three conditions they would say “a saheeh isnaad”, so as to alert the reader to the fact that they were only verifying that it met the first three conditions, and not the fourth and fifth, so that the reader would be aware of what this muhaddith meant.
Al-Haafiz ibn al-Salaah (may Allaah have mercy on him) said:
When they say “This hadeeth has a saheeh isnaad or a hasan isnaad” instead of “this is a saheeh hadeeth or a hasan hadeeth”, that is because it may be said that this hadeeth has a saheeh isnaad but it is not saheeh per se because it is shaadhdh (odd) or mu’allal (faulty). End quote.
Muqaddimah fi ‘Uloom al-Hadeeth (p. 23)
Ibn Katheer says:
The fact that the isnaad is deemed to be saheeh or hasan does not necessarily mean that the same applies to the text, because it may be shaadhdh (odd) or mu’allal (faulty). end quote.
Ikhtisaar ‘Uloom al-Hadeeth (p. 43).
Al-‘Iraaqi said in his Alfiyyah:
The ruling that the isnaad is saheeh or hasan does not necessarily apply to the text. End quote.
Al-Tabsirah wa’l-Tadhkirah (1/107).
Nevertheless, there may be an exception to this differentiation if it is known that a particular imam does not make this distinction between the two terms “a saheeh isnaad” and “a saheeh hadeeth” in his terminology. An imam – especially if he is one of the earlier scholars – may say “a saheeh isnaad” when he means that the hadeeth itself is saheeh, and that it meets all five conditions.
Al-Haafiz Ibn al-Salaah (may Allaah have mercy on him) said:
But a reliable scholar may say in his book “it has a saheeh isnaad” and not mention any ‘illah (fault), or criticize it, so it may be understood that he deems it to be saheeh in and of itself, because the absence of any ‘illah (fault) or qaadih (flaw) is the basic principle. And Allaah knows best. End quote.
Muqaddimah fi ‘Uloom al-Hadeeth (p. 23).
Al-Haafiz Ibn Hajar (may Allaah have mercy on him) said:
It seems to me that the correct view is that a distinction should be made between the one who differentiates when describing hadeeth as saheeh, stating it in either specific or general terms, and the one who does not do so.
The one who is known from studying his books to make this distinction should be viewed accordingly, so when he speaks in general terms it should be understood as referring to both the isnaad and the matn, and when he speaks in specific terms it should be understood as referring to the isnaad only.
And it maybe said concerning the one who is known to describe hadeeth only in specific terms all the time what we quoted above. End quote.
Al-Nukat ‘ala Ibn al-Salaah (1/474).
And Allaah knows best.