ENOfficial
Asma' daughter of Yazid b. as-Sakan reported the Prophet (ﷺ) a saying, "The dajjal will remain in the earth forty years, a year being like a month, a month like a week, a week like a day, and a day like the time it takes to burn a palm-branch." It is transmitted in Sharh as sunna.
Source: sunnah.com
Other translations
Arabic
وَعَن أَسمَاء بنت يزِيد بن السَّكن قَالَتْ: قَالَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «يَمْكُثُ الدَّجَّالُ فِي الْأَرْضِ أَرْبَعِينَ سَنَةً السَّنَةُ كَالشَّهْرِ وَالشَّهْرُ كَالْجُمُعَةِ وَالْجُمُعَةُ كَالْيَوْمِ وَالْيَوْمُ كَاضْطِرَامِ السَّعَفَةِ فِي النَّارِ» . رَوَاهُ فِي «شَرْحِ السُّنَّةِ»
sunnah.com