Brahma Vijigyaasa

अन्नं ब्रह्मेति वैजानात | अन्नाध्येवा खल्विमानी भूतानि जायन्ते |

अन्नेना जातानी जीवन्ति | अन्नं  प्रय्त्यभिसंविशंती  इति |  

तद्विग्नाया | पुनरेवा वरुणं पितर मुपससार | 

अदिही भगवो ब्रह्मेति | तागुम होवाचा | 

तपसा ब्रह्म विजिग्न्यासस्व | तपो ब्रह्मेति |

स तापोतप्य्त | स तपस्तप्त्वा |

Annam brahmEti vaijaanaat, AnnadhyEva khalvimaani bhootani jaayante |
annena jaataani jeevanti, annam prayatyabhisamvishanti iti|
tadvigaaya, punareva varuNam pitaramupasasaara |
adhIhi BhagavO brahmeti | tagum hOvaacha |
tapasa brahma vijigyaasasva, tapO brahmeti |
sa tapotapyata, sa tapastaptvaa |

The above shloka is from the Taittareeya upanishat.

Bhrugu is the son of VaruNa, who asks his father where do I find Brahma (God), where is this? whether it is in the soul, eyes, ears, mind, mouth etc without which the beings (whichever has life on the earth) can't live without or from which the beings lead the life.

VaruNa replies, go ahead and do the research upon it. Do the tapas (research/analyze/pray/meditate/seek) about the Brahma  (the supreme soul) with a vishesha jigyaasa ( i.e, understand that it is great or special and you have the mind of a child to seek with). He continues you'll see Brahma by conducting tapas and hence mentions to have the heat and the urge to do the tapas and to see the Brahma have the hunger moving until you are satisfied that you have understood.

Bhrugu does the meditation and research and comes up to VaruNa stating that Annam (Food) is the Brahma (God), without which one cannot live, but then he also finds out that without food one can live upto many days, so it cannot be Brahma and again goes to Tapas as directed, guided, suggested and taught by his father...