Sage Vasishtha's explanation about Sage Vishwamitra to King Dasharatha

इक्ष्वाकूणां कुले जातः साक्षाद्धर्म इवापरः
धृतिमान्सुव्रतः श्रीमान् न धर्म हातुमर्हसि
त्रीषु लोकेषु विख्यातो धर्मात्मा इति राघवः
स्वधर्म प्रतिपद्यस्व न अधर्म वोढुमर्हसि
संश्रुत्यैवं करिश्यामीत्यकुर्वाणस्य राघव
इष्टापूर्तवधो भूयात्तस्माद्रामं विसर्जय
कृतास्त्रमकृतास्त्रं वा नैनं शक्ष्यंति राक्षसाः
गुप्तं कुशिकपुत्रेण ज्वलनेनामृतं यथा
एष विग्रहवान् धर्म एष वीर्यवतां वरः
एष बुद्धयाधिको लोके तपसस्च परायणं
एषो अस्त्रान्विविधान्वेत्ति त्रैलोक्य सचराचरे
नैनमन्यः पुमान्वेत्ति न च वेत्स्यंति के चन
न देवा नर्षयः के चिन्नासुरा न च राक्षसाः
गंधर्ववक्षप्रवराः सकिंनरमहोरगाः
सर्वास्त्राणी कृशाश्वस्य पुत्राः परमधार्मिकाः
कौशिकाय पुरा दत्ता यदा राज्यं प्रशासति
एवं वीर्यो महातेजा विश्वामित्रो महातपाः
न रामगमने राजन्संशयं गंतुमर्हसि

ikShvAkUNAM kulE jAtaH sAkShAddharma ivAparaH

dhRutimAnsuvrataH SrImAn na dharma hAtumarhasi

trIShu lOkEShu viKyAtO dharmAtmA iti rAGavaH

svadharma pratipadyasva na adharma vODhumarhasi

saMSrutyaivaM kariSyAmItyakurvANasya rAGava

iShTApUrtavadhO BUyAttasmAdrAmaM visarjaya

kRutAstramakRutAstraM vA nainaM SakShyaMti rAkShasAH

guptaM kuSikaputrENa jvalanEnAmRutaM yathA

ESha vigrahavAn dharma ESha vIryavatAM varaH

ESha buddhayAdhikO lOkE tapasasca parAyaNaM

EShO astrAnvividhAnvEtti trailOkya sacarAcarE

nainamanyaH pumAnvEtti na ca vEtsyaMti kE cana

na dEvA narShayaH kE cinnAsurA na ca rAkShasAH

gaMdharvavakShapravarAH sakiMnaramahOragAH

sarvAstrANI kRuSASvasya putrAH paramadhArmikAH

kauSikAya purA dattA yadA rAjyaM praSAsati

EvaM veeryO mahaatEjaa vishwaamitrO mahaatapaaH

na raamagamanE raajansaMshayaM gaMtumarhasi

Shloka Translation

Those born in the clan of ikshwaku are the epitome of Righteousness

You having great mind and doing good, why would you not respect the Dharma

It is famous in the three worlds that the Raghu Dynasty kings are the great souls of Dharma

When it comes to self-righteousness, why should you take the path of Non-righteousness

Hence after learning about what the earlier kings of the Raghava dynasty have done before

Kill your internal desire and then send Rama to do what is right

Even if they do or not do anything about those demons

Which is hidden as the treasure of the son of Kushika

Who is the idol of Dharma and the boon for one’s valour

He is well versed with his intellect which he has gained from deep meditation

He is a learned on various weapons used by the movables and immovable in the three worlds

There are no men who is equivalent to him that I can recall

There are no Gods, no Sages, no Asuras, no Demons, no kings, no Snakes,

And all of them together are just a small piece in front of him due to his height of righteousness

He has renounced the kingdom that you are ruling today

Such is the valour of the great enlightened one called vishwaamitra

Hence do not doubt about the path that Rama will be taking

The above verses are available in the 20th Sarga of Valmiki Maharshi's Ramayana where sage Vasishtha explains to the Dasharatha as to how Rama is in the safer hands, while explaining about the details of the enlightened sage Vishwamitra. He explains the path of his righteousness and mentions that there is no parallel for him in all the three worlds when it comes to the Dharma (righteousness) and without hesitation he should be sending Rama alongwith Vishwamitra and  have no doubts about the path that Rama would be taking under the guidance of Vishwamitra. He summarizes basically that he can truly trust the mentor that Rama has got and believe that his son would learn the path of righteousness through him.