'Alqamah Radhiyallahu anhu relates:
"I asked Aayeshah Radhiyallahu anha: 'Did Rasulullah Sallallahu 'Alayhi Wasallam fix a day for 'Ibaadah? She replied: 'The practices of Rasulullah Sallallahu 'Alayhi Wasallam was of a continuous nature. Who among you have the strength, which Rasulullah Sallallahu 'Alayhi Wasallam had?'" (FR)
English reference (FR): Book 42, Hadith 293 (FR)
Arabic reference (FR): Book 43, Hadith 310 (FR)