Valmiki Ramayana Bala Kanda Sarga 57 Shloka 12
Original Shlokaस वसिष्ठं समाहूय कथयामास चिन्तितम्। अशक्यमिति चाप्युक्तो वसिष्ठेन महात्मना।।1.57.12।।
1 source checked for this shloka
स: he, वसिष्ठम् Vasishta, समाहूय summoning, चिन्तितम् his intention, कथयामास narrated, महात्मना by the magnanimous, वसिष्ठेन by Vasishta, अशक्यमिति not capable so, उक्त: अपि spoken also.
Summoning Vasishta he (Trisahnku) communicated his intention, but the great Vasishta said it was not possible.