Salam,
Bismillah.
Bismillah.
Narrated Aisha:
the mother of the believers: Allah's Apostle during his illness prayed at his house while sitting whereas some people prayed behind him standing. The Prophet beckoned them to sit down. On completion of the prayer, he said, 'The Imam is to be followed: bow when he bows, raise up your heads (stand erect) when he raises his head and when he says, 'Sami a-l-lahu liman-hamida ' (Allah heard those who sent praises to Him) say then 'Rabbana wa laka-l-hamd' (O our Lord! All the praises are for You), and if he prays sitting then pray sitting."
The provision of this Hadith has been abrogated by the last action of the Prophet (SAW). See next Hadith.
Narrated Anas bin Malik:
Once Allah's Apostle rode a horse and fell down and the right side (of his body) was injured. He offered one of the prayers while sitting and we also prayed behind him sitting. When he completed the prayer, he said, "The Imam is to be followed. Pray standing if he prays standing and bow when he bows; rise when he rises; and if he says, 'Sami a-l-lahu-liman hamida, say then, 'Rabbana wa Lakal-hamd' and pray standing if he prays standing, and pray sitting (all of you) if he prays sitting."
Humaid said: The saying of the Prophet "Pray sitting, if he (Imam) prays sitting" was said in his former illness (during his early life) but the Prophet prayed sitting afterwards (in the last illness) and the people were praying standing behind him and the Prophet did not order them to sit. We should follow the latest actions of the Prophet.
Similar Hadith has been covered before. Read here.
Here's when we realize how important knowledge of Hadith is. The sciences of Hadith. It's quite a vast subject, I must say. Just to give you an example from `Ilm-ur-Rijaal: a Hadith has two parts: the chain of narrators (sanad) and the text (matn). Chain of narrators in Imaam Bukhari's time usually had 3-6 narrators. In order for a Hadith to be claimed Saheeh (authentic), it's important to check each narrator's `aqeedah, character, scholars' opinion about them, memory etc. Imaam Bukhari used to check each narrator for each Hadith, and when he was sure that each narrator was an honest, reliable person having a good memory etc., only then would he include the Hadith in his book. Imagine! He did the same check for more than 7000 Ahadith! O_O
This is just a tiny bit. There's a LOT more to what we call `Ulum-ul-Hadith.
More on Hadith Sciences here.
Wassalam.
