You need not avoid daily noise and seek out a quiet place. Just sweep your breast clean of the ordinary knowledge and views you have accumulated every day, and fill it with the phrase Amituofo. Try to become identified with it (tijiu = 體究) totally. Always generate the doubt, “Who after all is this person doing nianfo?” (Zhege nianfode bijing shi shui = 這個念佛的畢竟是誰). Dwell on this question constantly. You should not discriminate between existence and nonexistence. Neither should you purposely wait for awakening. The least bit of delusive thought will create obstacles. Empty your chest of everything. In walking, standing, sitting, or lying, in either solitude or company, leisure or engagement, always make your right thoughts succeed one another, your mind uninterrupted. After a long time, your effort will become pure and concentrated. There will naturally be quietude and ease, and then samadhi will appear. If you cannot achieve pure and single right-mindfulness and if torpor and distraction arise, do not drive them away consciously. Drop the huatou [Amituofo], turn the illuminating light of the mind inward, and find the source from which torpor and distraction come. As soon as they are caught by illumination, delusion and torpor will come to a stop immediately. When you persist in this way without sliding backward, one day all of a sudden the ball of doubt (yituan = 疑團) will be smashed to smithereens and your worries of endless kalpas will dissolve away like ice.

Chushi Fanqi (楚石梵琦 1296 – 1370) as quoted in “The Renewal of Buddhism in China” by Chün-fang Yü (Chapter Three: Zhuhong and the Joint Practice of Pure Land and Chan)
https://cup.columbia.edu/book/the-renewal-of-buddhism-in-china/9780231198530