مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4181
Musnad of Abdullah bin Mas'ood
It was narrated that Ibn Mas'ood said: We did not fast Ramadan at the time of The Messenger of Allah (ﷺ) with twenty-nine days more often than we fasted it with thirty.
Musnad Ahmad 4209Hasan because of corroborating evidence; this is a da’eef is