1"Bhikkhus, in the past a tortoise [n.184] Text uses both words, kummo kacchapo. See SN17:3. was searching for food along the bank of a river one evening. On that same evening a jackal was also searching for food along the bank of that same river. When the tortoise saw the jackal in the distance searching for food, sn.iv.178 it drew its limbs and neck inside its shell and passed the time keeping still and silent. [n.185] Apposukko tuṇhı̄bhūto saṅkasāyati. As at SN21:4.

"The jackal had also seen the tortoise in the distance searching for food, so he approached and waited close by, thinking, ‘When this tortoise extends one or another of its limbs or its neck, I will grab it right on the spot, pull it out, and eat it.’ But because the tortoise did not extend any of its limbs or its neck, the jackal, failing to gain access to it, lost interest in it and departed.

2"So too, bhikkhus, Māra the Evil One is constantly and continually waiting close by you, thinking, ‘Perhaps I will gain access to him through the eye or through the ear … or through the mind.’ Therefore, bhikkhus, dwell guarding the doors of the sense faculties. Having seen a form with the eye, do not grasp its signs and features. Since, if you leave the eye faculty unguarded, evil unwholesome states of covetousness and displeasure might invade you, practise the way of its restraint, guard the eye faculty, undertake the restraint of the eye faculty. Having heard a sound with the ear … Having smelt an odour with the nose … Having savoured a taste with the tongue … Having felt a tactile object with the body … Having cognized a mental phenomenon with the mind, do not grasp its signs and features. Since, if you leave the mind faculty unguarded, evil unwholesome states of covetousness and displeasure might invade you, practise the way of its restraint, guard the mind faculty, undertake the restraint of the mind faculty.

"When, bhikkhus, you dwell guarding the doors of the sense faculties, Māra the Evil One, failing to gain access to you, will lose interest in you and depart, just as the jackal departed from the tortoise." sn.iv.179

3Drawing in the mind's thoughts
As a tortoise draws its limbs into its shell,
Independent, not harassing others, fully quenched,
A bhikkhu would not blame anyone. [n.186] The verse = I, v. 34. As the verse is not preceded by the usual sentence stating that the Buddha spoke it on this occasion, it seems the redactors of the canon have tacked it on by reason of the tortoise simile.

1"Bhūtapubbaṁ, bhikkhave, kummo kacchapo sāyanhasamayaṁ anunadītīre gocarapasuto ahosi. Siṅgālopi kho, bhikkhave, sāyanhasamayaṁ anunadītīre gocarapasuto ahosi. Addasā kho, bhikkhave, kummo kacchapo siṅgālaṁ dūratova gocarapasutaṁ. Disvāna soṇḍipañcamāni aṅgāni sake kapāle samodahitvā appossukko tuṇhībhūto saṅkasāyati.

Siṅgālopi kho, bhikkhave, addasa kummaṁ kacchapaṁ dūratova gocarapasutaṁ. Disvāna yena kummo kacchapo tenupasaṅkami; upasaṅkamitvā kummaṁ kacchapaṁ paccupaṭṭhito ahosi: ‘yadāyaṁ kummo kacchapo soṇḍipañcamānaṁ aṅgānaṁ aññataraṁ vā aññataraṁ vā aṅgaṁ abhininnāmessati, tattheva naṁ gahetvā uddālitvā khādissāmī’ti. Yadā kho, bhikkhave, kummo kacchapo soṇḍipañcamānaṁ aṅgānaṁ aññataraṁ vā aññataraṁ vā aṅgaṁ na abhininnāmi, atha siṅgālo kummamhā nibbijja pakkāmi, otāraṁ alabhamāno.

2Evameva kho, bhikkhave, tumhepi māro pāpimā sātataṁ samitaṁ paccupaṭṭhito: ‘appeva nāmāhaṁ imesaṁ cakkhuto vā otāraṁ labheyyaṁ … pe … jivhāto vā otāraṁ labheyyaṁ … pe … manato vā otāraṁ labheyyan’ti. Tasmātiha, bhikkhave, indriyesu guttadvārā vihāratha. Cakkhunā rūpaṁ disvā mā nimittaggāhino ahuvattha, mā anubyañjanaggāhino. Yatvādhikaraṇamenaṁ cakkhundriyaṁ asaṁvutaṁ vihārantaṁ abhijjhādomanassā pāpakā akusalā dhammā anvāssaveyyuṁ, tassa saṁvarāya paṭipajjatha, rakkhatha cakkhundriyaṁ, cakkhundriye saṁvaraṁ āpajjatha. Sotena saddaṁ sutvā … ghānena gandhaṁ ghāyitvā … jivhāya rasaṁ sāyitvā … kāyena phoṭṭhabbaṁ phusitvā … manasā dhammaṁ viññāya mā nimittaggāhino ahuvattha, mā anubyañjanaggāhino. Yatvādhikaraṇamenaṁ manindriyaṁ asaṁvutaṁ vihārantaṁ abhijjhādomanassā pāpakā akusalā dhammā anvāssaveyyuṁ, tassa saṁvarāya paṭipajjatha, rakkhatha manindriyaṁ, manindriye saṁvaraṁ āpajjatha.

Yato tumhe, bhikkhave, indriyesu guttadvārā viharissatha, atha tumhehipi māro pāpimā nibbijja pakkamissati, otāraṁ alabhamāno – kummamhāva siṅgāloti.

3Kummova aṅgāni sake kapāle,
Samodahaṁ bhikkhu manovitakke;
Anissito aññamaheṭhayāno,
Parinibbuto nūpavadeyya kañcī"ti.

Tatiyaṁ.