SB 10.71.6

dvai-rathe sa tu jetavyo
 mā śatākṣauhiṇī-yutaḥ
brāhmaṇyo ’bhyarthito viprair
 na pratyākhyāti karhicit
dvai-rathe — in combat involving only two chariots; saḥ — he; tu — but; jetavyaḥ — is to be defeated; — not; śata — by one hundred; akṣauhiṇī — military divisions; yutaḥ — joined; brāhmaṇyaḥ — devoted to brahminical culture; abhyarthitaḥ — entreated; vipraiḥ — by brāhmaṇas; na pratyākhyāti — does not refuse; karhicit — ever.
He will be defeated in a match of single chariots, not when he is with his hundred military divisions. Now, Jarāsandha is so devoted to brahminical culture that he never refuses requests from brāhmaṇas.

It might be argued that since only Bhīma could equal Jarāsandha in personal strength, Jarāsandha would be more powerful when supported by his huge army. Therefore, Uddhava here recommends single combat. But how could Jarāsandha be persuaded to give up the support of his powerful army? Here Uddhava gives the clue: Jarāsandha will never refuse a request from brāhmaṇas, since he is devoted to brahminical culture.