It wasnarrated from Hafsah that the Messenger of Allah (ﷺ) said:
"Thereis no fast for the one who did not make it incumbent uponhimselffrom the night before." (AR)
English reference (AR): Vol. 1, Book 7, Hadith 1700 (AR)
Arabic reference (AR): Book 7, Hadith 1770 (AR)