Dought & clear, - What are the ahaadeeth that may be used as shar’i evidence?.

What are the ahaadeeth which may be accepted and used as evidence in sharee'ah?.
Praise be to Allaah.
The ahaadeeth which must be accepted and taken as evidence are the
acceptable ahaadeeth: those which are saheeh or hasan. As for da'eef
(weak) and false ahaadeeth, it is not permissible to use them as
evidence with regard to shar'i rulings.
Al-Imam al-Shaafa'i said inal-Risaalah(p. 463):
It is obligatory to accept a report once it is proven, even if the
imams did not act upon this report. End quote. In other words: once a
hadeeth is proven to be from the Prophet(peace and blessings of Allaah
be upon him), it is obligatory to act upon it.
'Abd-Allaah ibn al-Imam Ahmad ibn Hanbal said:
I asked my father about a man who has books which contain the words of
the Messenger of Allaah(peace and blessings of Allaah be upon him) and
the Sahaabah and Taabi'een, but the man does not know how to recognize
da'eef (weak) and matrook (rejected) ahaadeeth, and he cannot tell a
strong isnaad from a weak one. Is it permissible for him to act upon
whatever he wants and to choose reports and issue fatwas and act on
that basis?
He said: he should not do anything until he finds out which ahaadeeth
are sound and may be acted upon, so that he will be acting upon a
sound basis. He should ask the scholars about that. End quote.
I'laam al-Muwaqqi'een(4/179).
Imam Muslim (may Allaah have mercy on him) said:
You should note, may Allaah have mercy on you, that knowledge of
hadeeth and determining which are sound and which are unsound is the
role of the scholars of hadeeth only, because they are the ones who
have memorized the people's reports and they know them well, unlike
others. So the basic principle on which they base their beliefs is the
Sunnahs and reports which were transmitted from one era to the next
from our Prophet(peace and blessings of Allaah be upon him) until the
present day. End quote.
Al-Tamyeez, p. 218
Imam al-Sarkhasi (may Allaah have mercy on him) said:
Not following a saheeh hadeeth from the Messenger of Allaah(peace and
blessings of Allaah be upon him) is haraam, just as doing what is
contrary to it is haraam. End quote.
Usool al-Sarkhasi(2/7).
Al-Nawawi (may Allaah have mercy on him) said:
The scholars said: Ahaadeeth are of three types: saheeh (sound), hasan
(good) and da'eef (weak). They said: It is only permissible to quote
as evidence concerning rulings those ahaadeeth which are saheeh or
hasan. As for those which are da'eef, it is not permissible to quote
them as evidence with regard to rulings or beliefs, but it is
permissible to narrate them and act upon them with regard to matters
other than rulings, such as stories, virtuous deeds, and offering
encouragements and warnings. End quote.
Al-Majmoo'(1/98).
Al-Haafiz Ibn Rajab (may Allaah have mercy on him) said:
With regard to the imams and fuqaha' of ahl al-hadeeth, they follow
the saheeh hadeeth wherever it is. End quote.
Fadl 'Ilm al-Hadeeth(p. 57).
Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) said:
It is not permissible to rely in matters of sharee'ah on da'eef
ahaadeeth which are not saheeh or hasan. End quote.
Majmoo' al-Fataawa(1/250).
Al-'Allaamah Zakariya al-Ansaari (may Allaah have mercy on him) said:
The one who wants to quote as evidence a hadeeth from the Sunans or
Musnads, if he is qualified to distinguish between what may be quoted
as evidence and what may not, then he should not quote it as evidence
unless he examines its isnaad and its narrators. Otherwise if he can
find one of the imams who classed it as saheeh or hasan, he may follow
him, otherwise he should not quote it as evidence.And Allaah knows
best.