What is the difference between sunnah and hadith?

The meaning of Sunnah

Sunnah linguistically refers to several possible meanings; a way issued by earlier peoples and followed by later ones, circularity of face, image of someone or something, the nature or attribute and the story of a certain nation.

Classical scholars differ on the meaning of the Arabic term Sunnah. Scholars of Hadith consider Sunnah as everything narrated concerning the life of the Prophet (saw) as well as opinions of the companions and their successors. Scholars of Usul al-Fiqh conceder only what the Prophet did, said or approved as Sunnah. Scholars of jurisprudence, generally, use the term Sunnah to refer to what is recommended (Mustahab or Mandub). Theologians were more concerned with orthodox theological teachings and innovations (bid'ah) in the creed (i'tiqad).

The Definition of Hadith

Hadith linguistically means a telling or information. The lexicon Mu'jam al-Ma'ani al-Jami' says:

كلُّ مَا يُتَحَدَّثُ بِهِ مِنْ كَلاَمٍ وَخَبَرٍ
"Every spoken matter whether it is general talking or a report."

Hadith technically means everything narrated concerning the life of the Prophet (saw) before or after the initiation of revelation. This includes his sayings, acts, approvals, attributes and other reports. It also includes what the companions narrated about the Prophet (al-Marfu') and their successors (al-Maqtu'):

مَا أُضِيفَ إِلَى النَّبِيِّ صَلَّى اللهُ عَلَيهِ وَسَلَّمَ قَوْلَا أَوْ فِعْلًا أَوْ تَقْريرًا.
"What has been attributed to the Prophet (saw) of a statement, an act or an approval." (Ibn Kathir, al-Ba'ith al-Hathith, Vol. 1, p. 45, al-Ibari, Nayl al-Amani, p. 27)

Discussion

We see the term Hadith equals the term Sunnah according to the definition presented by scholars of Hadith and scholars of Usul al-Fiqh. But the other two definitions of the Sunnah, i.e. the definition according to scholars of Fiqh and scholars I'tiqad, are exclusively for the Sunnah and can't be attributed to the Hadith.

Whilst the term hadith could refer to some theological meanings and may equal Sunnah when it is attributed to people of the right creed (Ahlu Al-Hadith or Ahlu al-Sunnah), it could not be attributed to individual subjects of the creed, nor the collective mutawatir way and guidance of the Prophet (saw) in religion (Sunnah).

Term Sunnah cannot also be attributed to individual narrations (hadiths), but a hadith could contradict the Sunnah in sense of the collective transmitted manner. The hadith is the narration, but the Sunnah is how the companions (ra) and their successors understood and performed it. (al-Fasawi, al-Ma'rifah, Vol. 1, p. 480)

Aisha (ra) said regarding the rituals of Hajj:

إِنَّمَا نَزَلَ رَسُولُ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ الْمُحَصَّبَ لِيَكُونَ أَسْمَحَ لِخُرُوجِهِ وَلَيْسَ بِسُنَّةٍ فَمَنْ شَاءَ نَزَلَهُ وَمَنْ شَاءَ لَمْ يَنْزِلْهُ ‏.‏
"The Messenger of Allah (saw) alighted at al-Muhassab so that it might be easier for him to proceed (to Medina). It is not a Sunnah. Anyone who desires may alight there, and anyone who does not want may not alight." (Sunan Abi Dawud 2008)

So the act was transmitted in hadith but it is not a part of the final Sunnah of the Prophet (saw) because it was contextually conditioned. For that reason, many scholars of hadith, such as Tirmidhi, included certain hadiths and then referred to what is the Sunnah of its understanding or ruling.

Regarding this point, al-Juhari (Maliki jurist and Muhadith, d. 381 A.H.) said:

السُّنَةُ الْمُتَقَدِّمَةُ مِنْ سُنَّةِ أَهْلِ الْمَدِينَةِ خَيْرٌ مِنَ الْحَديثِ
"The Sunnah of people of Medina is better than the hadith. (according to the Maliki Madhab)" (al-Juhari Musnad al-Muwatta', Vol. 1, p. 11)

In light of the previous discussion, we could grasp the intended meaning of a statement like:

سُفْيانُ الثَّوْرَِيُ إمَامٌ فِي السُّنَّةِ إمَامٌ فِي الْحَديثِ . وَشُعْبَةُ بْنُ الْحَجَّاجِ إمَامٌ فِي الْحَديثِ وَلَيْسَ بِإمَامٍ فِي السُّّّنَّةِ .
"Sufyan Thawri is a leading scholar in Sunnah and in Hadith, but Shu'bah ibn al-Hajaj is a leading scholar in hadith, not in Sunnah." (Mahdi, al-Jarh wa at-Ta'deel, Vol. 2, p. 19)

Conclusion

The Arabic terms Sunnah and Hadith are sometimes exchangeable and sometimes mean different and independent meanings depending on the discipline.

References

Ibn Kathir, al-B'ith al-Hathith
al-Ibari, Nayl al-Amani
Mu'jam al-Ma'ani al-Jami'
al-Fasawi, al-Ma'rifah
al-Juhari Musnad al-Muwatta'
Mahdi, al-Jarh wa at-Ta'deel

Further Reading

Imam Amin Ahsan Islahi, Difference Between Hadith And Sunnah: http://www.al-mawrid.org/index.php/articles/view/difference-between-hadith-and-sunnah1

The terms "Sunna" and "Ḥadīth" are often used interchangeably. This use is inaccurate. As I explained, "Sunna" denotes what the Prophet said, did, approved, and disapproved of, explicitly or implicitly. "Ḥadīth," on the other hand, refers to the reports of such narrations.

Furthermore, while "Ḥadīth" and "Sunna" are used synonymously because the Ḥadīth literature is the main source of the Sunna of the Prophet, it is not its only source. There are two other sources. First, the practices of the people of Medina were considered to have come from the Prophet. Medina is the city where the Prophet lived his last ten years, where most legislations of the new religion were revealed in the Qur'an or devised by the Prophet, and where the first three caliphs and most Companions continued to live. The assumption, which was effectively promoted by Mālik bin Anas (93/715-179/796), is that Medinese practice could not have come from other than the Prophet. Even what is attributed to Companions is linked to the Prophet on the assumption that these elite Muslims could have only behaved and legislated in accordance with what they learned from their Master. Malik even rejected ḥadīths that contradicted the established practices of the people of Medina.