Hadith 501
يصلي الضحي حتي نقول لا يدعها و يدعها حتي نقول لا يصليها
"The Prophet (peace be upon him) would perform the Duha prayer to such an extent that we would say, 'Now he will never leave it,' and then he would leave it to such an extent that we would say, 'Now he will never perform it.'"
