Yes, You are looking for Rigveda 1.32.1
The verse of Agnipurana you're talking about in the question might be Agnipurana 259.14 (259th chapter from Agnipurna is "Rigvidhanam") quoting from sa.wikisource.org: (Transliterated into IAST):
ṛgbhiḥ ṣoḍaśabhiḥ kuryyādindrasyeti dine dine |
hihaṇyastūpamityetajjapan śatrūn prabādhate || 259.14 ||
After locating this verse from Sanskrit Wikisource, I've tried reading translation of this verse from a book on English translation of Agnupurana from West Bengal Dspace as provided by 'The Destroyer' in this answer and here is what I find: (Page no. 730)

As you can see, in the notes, they're giving the link of this Agnipurana's saying to Rigveda hymns : Rigveda 1.32.1
So, what you are looking is 32nd Sukta of 1st Mandala of Rigveda