464 – Talhah ibn ʿAbd Allah ibn ʿAwf (may Allah be pleased with him) said: “I prayed the funeral prayer behind Ibn ʿAbbās. He recited the Opening Chapter of the Book, then said, ‘So that you may know, it is sunnah.’” Reported by al-Bukhārī (1).

Vocabulary of the ḥadith:
• “so that you may know”: the prefixed lām is the lām of command, so the verb is in the jussive; it may also be taken as the lām of purpose, in which case the verb is in the subjunctive.
• “that it is sunnah”: i.e. a practice taken from the Prophet ﷺ. What is meant is not the later juristic contrast between sunnah and obligation, for that technical usage arose after the early generations.

Points derived from the ḥadiths:
1 – Ḥadith no. 462 shows that the takbīrs in the funeral prayer are four, and that this was the settled understanding among the Companions. Zayd ibn Arqam, however, once added a fifth takbīr; when they asked him about the addition he said, “The Messenger of Allah ﷺ used to pronounce it.”
As for the report of Saʿīd ibn Manṣūr that ʿAlī (may Allah be pleased with him) added two takbīrs—making six—when he prayed over Sahl ibn Ḥunayf, it seems they questioned him, whereupon he explained that the deceased was one of the veterans of Badr, and the people of Badr possess a superiority over others.
Al-Nawawī said: “The ummah has unanimously agreed that the takbīrs are four, with neither addition nor omission.”
2 – Ḥadith no. 463 indicates that the Prophet ﷺ used to pronounce four takbīrs over the deceased