بُلُوغُ الْمَرَامِ
Bulugh al-Maram 162
The Book of Prayer
وَلِمُسْلِمٍ عَنْ عَائِشَةَ نَحْوَهُ, وَقَالَ: "سَجْدَةً" بَدَلَ "رَكْعَةً". ثُمَّ قَالَ: وَالسَّجْدَةُ إِنَّمَا هِيَ اَلرَّكْعَةُ [1] .
Muslim reported the same above Hadith in another version narrated by 'Aishah (RA), who narrated 'Sajdah (prostration)' instead of 'Rak'a (prayer unit)' and then he (Muslim) said: "A Sajdah implies a Rak'a."
Sunnah.com reference: Book 2, Hadith 12