Sunan Abi Dawud 2322
سنن أبي داود#2322SahihNarrated Abdullah ibn Mas'ud: We kept fast for twenty-nine days along with the Prophet (ﷺ) more often than we kept fast for thirty days
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Shuaib Al ArnautSahih Lighairihi
Zubair Ali ZaiIsnaad Hasan
In-book reference: 14:10