On one occasion the Blessed One was staying near Kapilavatthu at the Banyan Park. Then many Sakyan lay followers, it being the Uposatha day, went to the Blessed One. On arrival, having bowed down to him, they sat to one side. As they were sitting there, the Blessed One said to them, "Sakyans, do you observe the eight-factored uposatha?"
"Sometimes we do, lord, and sometimes we don't."
"It's no gain for you, Sakyans. It's ill-gotten, that in this life so endangered by grief, in this life so endangered by death, you sometimes observe the eight-factored uposatha and sometimes don't.
"What do you think, Sakyans. Suppose a man, by some profession or other, without encountering an unskillful day, were to earn a half-kahapana. Would he deserve to be called a capable man, full of initiative?"
"Yes, lord."
"Suppose a man, by some profession or other, without encountering an unskillful day, were to earn a kahapana... two kahapanas... three... four... five... six... seven... eight... nine... ten... twenty... thirty... forty... fifty... one hundred kahapanas. Would he deserve to be called a capable man, full of initiative?"
"Yes, lord."
"Now what do you think: earning one hundred, one thousand kahapanas a day; saving up his gains, living for one hundred years, would a man arrive at a great mass of wealth?"
"Yes, lord."
"Now what do you think: would that man, because of that wealth, on account of that wealth, with that wealth as the cause, live sensitive to unalloyed bliss for a day, a night, half a day, or half a night?"
"No, lord. And why is that? Sensual pleasures are inconstant, hollow, false, deceptive by nature."
"Now, Sakyans, there is the case where a disciple of mine, spending ten years practicing as I have instructed, would live sensitive to unalloyed bliss for a hundred years, a hundred centuries, a hundred millennia. And he would be a once-returner, a non-returner, or at the very least a stream-winner.
"Let alone ten years, there is the case where a disciple of mine, spending nine years... eight years... seven... six... five... four... three... two years... one year practicing as I have instructed, would live sensitive to unalloyed bliss for a hundred years, a hundred centuries, a hundred millennia. And he would be a once-returner, a non-returner, or at the very least a stream-winner.
"Let alone one year, there is the case where a disciple of mine, spending ten months... nine months... eight months... seven... six... five... four... three... two months... one month... half a month practicing as I have instructed, would live sensitive to unalloyed bliss for a hundred years, a hundred centuries, a hundred millennia. And he would be a once-returner, a non-returner, or at the very least a stream-winner.
"Let alone half a month, there is the case where a disciple of mine, spending ten days & nights... nine days & nights... eight... seven... six... five... four... three... two days & nights... one day & night practicing as I have instructed, would live sensitive to unalloyed bliss for a hundred years, a hundred centuries, a hundred millennia. And he would be a once-returner, a non-returner, or at the very least a stream-winner.
"It's no gain for you, Sakyans. It's ill-gotten, that in this life so endangered by grief, in this life so endangered by death, you sometimes observe the eight-factored uposatha and sometimes don't."
"Then from this day forward, lord, we will observe the eight-factored uposatha."
Siehe auch: AN 3.70; AN 8.43; Ud 2.10; "Uposatha Observance Days" in the Path to Freedom Pages.