Krishna Yajur Veda 7.4.19 -

So the wise priest returned to the altar. He took the two sticks and bound them with a single thread of darbha grass. He laid them crosswise, then side by side, then pressed them together with his palms. He recited Krishna Yajur Veda 7.4.19: “You two are twins born of the same womb of sacrifice. Do not separate. Burn as one. Speak to the gods with a single tongue.” The sticks fused. The flame roared up, blue at the base, red at the heart, white at the tip. And the gods saw in that flame the image of the eternal couple: Dyaus (heaven, father) and Prithivi (earth, mother), united in the fire of the altar.

When the priests obeyed, the fire split into two weak flames that hissed at each other like enemies. The sacrifice failed. Crops withered. Rain stopped. krishna yajur veda 7.4.19

The verse (often cited in the Taittirīya Saṃhitā ) deals with a ritual concerning the Vedī (sacrificial altar) and the placement of two kinds of fuel sticks ( samidhs ) — one from the Aśvattha (sacred fig) and one from Nyagrodha (banyan). The verse states that these two are placed together, and they are addressed as “twin-born” or “paired.” So the wise priest returned to the altar

Prajapati looked deep into the sacrifice. He saw that the fire was lonely. “The fire needs kinship,” he said. “Not just fuel, but family.” He recited Krishna Yajur Veda 7

That night, the first priest did as he was told. He took the Aśvattha stick (straight, hard, fire-hiding in its heart) and the Nyagrodha stick (soft, moist, life-giving in its sap). He laid them on the dying embers.