"सिद्धानं बुद्धानं" (Siddhāṇaṃ Buddhāṇaṃ) is a phrase that appears in Jain Prakrit texts, particularly in the context of prayers or salutations. In Jainism, "सिद्ध" (Siddha) refers to the liberated souls who have destroyed all karmas and attained moksha, while "बुद्ध" (Buddha) in Jain usage refers to those who have attained perfect knowledge (kevala jnana) and enlightenment (not to be confused with Gautama Buddha of Buddhism).

Another name or sutra where these terms are found is the Namokar Mantra (also called Navkar Mantra or Namaskar Mantra), the most fundamental prayer in Jainism. The mantra pays homage to five supreme beings:

1. Arihant (enlightened beings)
2. Siddha (liberated souls)
3. Acharya (spiritual leaders)
4. Upadhyaya (spiritual teachers)
5. Sādhu/Sādhvi (monks and nuns)

In the original Prakrit, an early form of the mantra includes:

णमो अरिहंताणं, णमो सिद्धाणं, णमो आयरियाणं, णमो उवज्झायाणं, णमो लोए सव्वसाहूणं।

Here, "णमो सिद्धाणं" means "I bow to the Siddhas," and "बुद्ध" can sometimes be included in extended forms or in other Jain stutis (hymns).

So, the Namokar Mantra is the sutra most closely related to the phrase "सिद्धानं बुद्धानं" in Jainism.