Bhagavad Gita : अध्याय 17 का श्लोक 19
मूढग्राहेणात्मनो यत्पीडया क्रियते तपः।परस्योत्सादनार्थं वा तत्तामसमुदाहृतम्॥
भावार्थ : जो तप मूढ़तापूर्वक हठ से, मन, वाणी और शरीर की पीड़ा के सहित अथवा दूसरे का अनिष्ट करने के लिए किया जाता है- वह तप तामस कहा गया है ॥19॥
And those penances and austerities which are performed foolishly by means of obstinant self-torture, or to destroy or injure others, are said to be in the mode of ignorance.
There are instances of foolish penance undertaken by demons like Hiraṇyakaśipu, who performed austere penances to become immortal and kill the demigods. He prayed to Brahmā for such things, but ultimately he was killed by the Supreme Personality of Godhead. To undergo penances for something which is impossible is certainly in the mode of ignorance.