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."

وَلِمُسْلِمٍ عَنْ عَائِشَةَ نَحْوَهُ, وَقَالَ: "سَجْدَةً" بَدَلَ "رَكْعَةً".‏ ثُمَّ قَالَ: وَالسَّجْدَةُ إِنَّمَا هِيَ اَلرَّكْعَةُ [1]‏ .‏