Al-Ahqaf (, ; "the sand dunes" or "the winding sand tracts") is the 46th chapter (surah) of the Qur'an with 35 verses (ayat). This is the seventh and last chapter starting with the Muqattaʿat letters Hāʼ Mīm. Regarding the timing and contextual background of the believed revelation (asbāb al-nuzūl), it is one of the late Meccan chapters, except for verse 10 and possibly a few others which Muslims believe were revealed in Medina. The chapter covers various topics: It warns against those who reject the Quran, and reassures those who believe; it instructs Muslims to be virtuous towards their parents; it tells of the Prophet Hud and the punishment that befell his people, and it advises Muhammad to be patient in delivering his message of Islam. A passage in verse 15, which talks about a child's gestation and weaning, became the basis by which some Islamic jurists determined that the minimum threshold of fetal viability in Islamic law would be about 25 weeks. The name of the chapter comes from verse 21, where Hud is said to have warned his people "by the sand dunes" (bī al-Ahqaf). Summary 1 The Quran a revelation from God 2-5 Creation a witness for God against idolaters and idolatry 6-7 Disbelievers charging Muhammad with forging the Quran 8 Muhammad, like other apostles, only a warner 9-10 Believing Jews confirm the Quran; unbelieving Jews call it an antiquated lie 11 The Quran confirms the Book of Moses 12-13 True believers, their happy condition 14-15 Obedient sons and true believers, their life here and hereafter 16-17 The conduct and fate of the disobedient son 18-20 Rewards and punishments bestowed in accordance with works The History of Hūd 21-27 The fate of the people of Hud (as), &c., a warning to Makkah The story of the Jinn listening to the Quran 28-31 The genii converted by hearing Muhammad recite the Quran 32-35 God able to raise the dead; Muhammad exhorted to patience and forbearance The chapter begins with a Muqattaʿat, the two-letter formula Hā-Mīm, the last of the seven chapters to do so. In the Islamic tradition, the meanings of such formulae at the beginnings of chapters are considered to be "known only to God". The following verses (2–9) warn against those who reject the Quran and reiterate the Quranic assertion that the verses of the Quran are revealed from God and were not composed by humans.