The Messenger of Allah ﷺ gave permission to the weaker people to leave Muzdalifa at night.
حدثنا عبد الرزاق أخبرنا معمر عن الزهري عن سالم
أن رسول الله ﷺ أذن لضعفة الناس من المزدلفة بليل
Its chain of transmission is sahih. It appears in al-Muntaqa 2602 and al-Qura by Muhibb Tabari p. 390, and both attributed it to Ahmad alone, so the more likely view is that it belongs among the additions beyond the six books. I did not find it in Majma al-Zawaid. Its meaning has already occurred repeatedly in the Musnad of Ibn Abbas, including at 1920, 3159, and 3304.