It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that when the opening verses of Surah al-Muzzammil were revealed, the Companions (may Allah be pleased with them) used to stand (in tahajjud) for as long as they would stand in the blessed month of Ramadan, until the last part of the surah was revealed. He said: Between the revelation of the first and the last part of this surah there was a period of about a year. This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.