This probably comes from The Analects, Book II: Wei Zheng: "The Master said, 'Learning without thought is labor lost; thought without learning is perilous.'" Confucius believed that learning (xue) and reflection (si) should be equally emphasized, and neither should be neglected.
Confucius believed that the combination of “learning” and “thinking” first requires thinking more and asking “why” during the learning process. He said: “He who does not say ‘What is to be done? What is to be done?’ — I do not know what to do with him.” (The Analects, Book XV, Wei Ling Gong). Confucius opposed passive, wholesale acceptance in learning and advocated maintaining reservations and being cautious about doubts. “Zi Zhang (a disciple of Confucius) asked about obtaining an official position. Confucius said: ‘Listen widely, set aside what is doubtful, and speak cautiously about the rest; then you will make few mistakes. Observe widely, set aside what is perilous, and act cautiously about the rest; then you will have few regrets. If your words have few mistakes and your deeds few regrets, an official position will naturally follow.’” (The Analects, Book II, Wei Zheng). Confucius’s disciple Zi Xia (a student known for his focus on learning) also said: “Learn broadly and be steadfast in your purpose; inquire earnestly and reflect on what is near at hand — Ren (Benevolence) lies in this.” (The Analects, Book XIX, Zi Zhang), which also emphasizes the inseparability of learning and thinking.
Confucius believed that the integration of "learning" (learning) and "thinking" (thinking) also required the ability to achieve comprehensive mastery and draw inferences from one instance to understand ten. Confucius said: "There may be those who act without knowing; I am not like that. To hear much, select what is good and follow it; to see much and remember it—this is the second level of knowledge." (The Analects, Book Seven, Chapter 28) While hearing and seeing much is important, what matters more is to connect the knowledge one has heard and seen. The Analects, Book Fifteen, Chapter 3 records: "The Master said: 'Ci (Zi Gong, a wealthy merchant and eloquent disciple), do you think I am one who learns much and remembers it?' He replied: 'Yes. Is it not so?' The Master said: 'No. I have one thread running through it all.'" This "one thread running through it all" (to be guided by one principle) refers to thinking. Also, according to The Analects, Book Five, Chapter 9: "The Master said to Zi Gong: 'Who is superior, you or Yan Hui (Confucius's most beloved disciple)?' He replied: 'How dare I compare myself with Hui? When he hears one thing, he understands ten; when I hear one thing, I understand two.' The Master said: 'You are not equal to him. I agree that you are not equal to him.'" To hear one and understand ten means to expand the limited knowledge one has acquired through thinking activities, in order to gain greater results. Additionally, Confucius said: "I do not resent Heaven, nor blame others. I learn from lower levels and reach higher understanding. Perhaps only Heaven knows me!" (The Analects, Book Fourteen, Chapter 35) Here, "learning from lower levels and reaching higher understanding" (learning the lower to reach the higher) also refers to the method of rational deduction, using basic knowledge acquired to grasp profound principles.
As a teacher, Confucius was careful to guide students in integrating thinking (thinking) throughout their learning process. He often enlightened them only when they were thoroughly perplexed and unable to find a solution on their own. He said: "I do not enlighten those who are not eager to learn, nor arouse those who are not anxious to give an explanation. If I hold up one corner of a square and a student cannot come back with the other three, I do not repeat the lesson." (The Analects, Book Seven, Chapter Eight) If students studied the Classic of Poetry (Shijing) but could not draw inferences or make connections, Confucius would not even discuss the book with them. The Analects, Book One, Chapter Fifteen records: "Zi Gong (a wealthy merchant and eloquent disciple) said: 'Poor without flattery, rich without arrogance—what do you think of that?' Confucius replied: 'Acceptable, but not as good as being poor yet joyful, rich yet fond of observing Li (Propriety).' Zi Gong said: 'The Book of Odes says: "As cut and filed, as ground and polished." Is this not what you mean?' Confucius said: 'Ci (Zi Gong's given name), now I can begin to discuss the Odes with you. I tell you one point, and you grasp the rest.'" Also, according to The Analects, Book Three, Chapter Eight, Confucius felt that Zi Xia (a disciple known for his literary refinement) was also "ready to discuss the Odes," because Zi Xia had connected the lines "Her cunning smile, her beautiful eyes, the plain ground for the colors" from the Classic of Poetry to Li (Propriety). Of course, merely daydreaming without learning would lead nowhere. Confucius had personal experience with "thinking without learning leads to peril." He said: "I once spent a whole day without eating and a whole night without sleeping, in order to think. It was of no use. It is better to learn." (The Analects, Book Fifteen, Chapter Thirty-One)
Confucius advocated a learning method that equally emphasized both study and reflection, which aligns with the principles of materialist epistemology. This proposition has inspired generations of Chinese scholars.