無量壽經優婆提舍願生偈註 1.91

1.91

問曰：幾時名為一念？答曰：百一生滅名一剎那，六十剎那名為一念。此中云念者，不取此時節也，但言憶念阿彌陀佛若總相若別相，隨所觀緣心無他想，十念相續名為十念。但稱名號亦復如是。

Question: How much time is called 'one thought'? Answer: A hundred and one arisings and ceasings is called a kṣaṇa; sixty kṣaṇas are called a single thought (eka-citta). What is called 'thought' here does not take this measurement of time; it simply means keeping Amitābha Buddha in mind, either in his general marks or specific marks, following the conditions of contemplation with no other thoughts in mind. A succession of ten such thoughts is called 'ten recitations.' Merely calling the name is also like this.