I do not know of the Messenger of Allah ﷺ singling out any day to fast, seeking its merit over other days, except the day of Ashura. Sufyan said on another occasion, "Except this day," meaning Ashura, "and this month," meaning the month of Ramadan.
حدثنا سفيان قال أخبرني عبيد الله بن أبي يزيد منذ سبعين سنة قال سمعت
ما علمت رسول الله ﷺ صام يوما يتحرى فضله على الأيام غير يوم عاشوراء وقال سفيان مرة أخرى إلا هذا اليوم يعني عاشوراء وهذا الشهر شهر رمضان
Its isnad is sahih. Sufyan bin Uyayna, the imam and hafiz, lived for 91 years, born in the year 107 and died in the year 198. Ubaydullah bin Abu Yazid Makki, his reliability was established earlier at 604, and he died in the year 126 at the age of 86. The hadith was narrated by Bukhari and Muslim, as in Muntaqa 2212, and it will come again at 2856.