Answer the following question: Given the following passage  "Besides emptiness, Mahayana schools often place emphasis on the notions of perfected spiritual insight (prajñāpāramitā) and Buddha-nature (tathāgatagarbha). There are conflicting interpretations of the tathāgatagarbha in Mahāyāna thought. The idea may be traced to Abhidharma, and ultimately to statements of the Buddha in the Nikāyas. In Tibetan Buddhism, according to the Sakya school, tathāgatagarbha is the inseparability of the clarity and emptiness of one's mind. In Nyingma, tathāgatagarbha also generally refers to inseparability of the clarity and emptiness of one's mind. According to the Gelug school, it is the potential for sentient beings to awaken since they are empty (i.e. dependently originated). According to the Jonang school, it refers to the innate qualities of the mind that expresses themselves as omniscience etc. when adventitious obscurations are removed. The "Tathāgatagarbha Sutras" are a collection of Mahayana sutras that present a unique model of Buddha-nature. Even though this collection was generally ignored in India, East Asian Buddhism provides some significance to these texts.",  answer the following question. Note that the answer is present within the text.  Question: What idea can be traced to Abhidharma and to Buddha in the Nikayes?
Answer:
tathāgatagarbha