There are three suttas (all named Bija Sutta): SN 22.54, SN 49.24, and AN 10.104.
It is helpful to note that kamma bija (or beeja) are created by vinnana: “Viññāna – What It Really Means” and “Sankhāra and Kammā, Viññāna and Kamma Beeja“.
July 28, 2018: Another important sutta in this context is, Pathamabhava Sutta (AN 3.76), which says: “Iti kho, ānanda, kammaṃ khettaṃ, viññāṇaṃ bījaṃ, taṇhā sneho..”
Translated: “Ānanda, deeds (kamma) are the field, viññāṇa is the seed, and craving (taṇhā) is the moisture..”