Mantra 13

स त्वमग्निꣳ स्वर्ग्यमध्येषि मृत्यो प्रब्रूहि तꣳ श्रद्दधानाय मह्यम् ।स्वर्गलोका अमृतत्वं भजन्त एतत् द्वितीयेन वृणे वरेण ॥ १३ ॥

In plain words

'You know, O Death, that fire leading to heaven -- declare it to me, who has faith, that fire by which the dwellers of the heavenly world attain immortality. This I choose as my second boon.'