Skandapurana 16.33.99

16.33.99

tatastena hṛdisthena proktā devī sarasvatī ..
prārthanīyo varo bhadre sūcīvaktratvamādarāt .. 99 ..

Then the goddess Sarasvatī was told by him who was in her heart:
“The boon to be requested with care, fair one, is that his mouth become like a needle.”