Can You Tell Me Some Verses From Hindu Scriptures Which Say Varna Is Not Based On Birth?
Here are 2 verses that clearly say that Varna is not dependent on birth in an endogamous group.
Yudhisthira said, " In human society, O mighty and highly intelligent serpent, it is difficult to ascertain one's caste, because of promiscuous intercourse among the four orders. This is my opinion. Men belonging to all orders (promiscuously) begat offspring upon women of all the orders. And of men, speech, sexual intercourse, birth and death are common. And to this the Rishis have borne testimony by using as the beginning of a sacrifice such expressions as -- of what caste server may be, we celebrate the sacrifice. Therefore, those that are wise have asserted that character is the chief essential requisite. .... whatsoever now conforms to the rules of pure and virtuous conduct, him have I, ere now, designated as a Brahmana.'
(Mahabharata Aranya Parva Section CLXXIX)
Maheshwara said, ‘..Neither birth, nor the purificatory rites, nor learning, nor offspring, can be regarded as grounds for conferring upon one the regenerate status. Verily, the conduct is the only ground. All Brahmanas in this world are Brahmanas in consequence of conduct. A Sudra, if he is established on good conduct, is regarded as possessed of the status of a Brahmana. The status of a Brahma, O auspicious lady [Uma], is equal wherever it exists. Even this is my opinion. He, indeed, is a Brahmana in which the status of Brahma exists – that condition which is bereft of attributes and which has no stain attached to it. of human beings in four orders dependent on birth is only for purposes of classification. The boon giving Brahma, when he created all creatures, himself said that the distribution of human beings in four orders dependent on birth is only for purposes of classification.'
Mahabharata Anusasana Parva Section CXLIII
चातुर्वर्ण्यं मया सृष्टं गुणकर्मविभागशः।
तस्य कर्तारमपि मां विद्ध्यकर्तारमव्ययम्।।4.13।।
The four varna were created by me based on Guna-karma(intrinsic aptitude i.e. what you do), however even though I am the cause of that intrinsic aptitude, know that I am without agency.
This is from Shreemad Bhagvat Gita Chapter 4, shlok 13.