Srimad Bhagavatam Canto 06, Chapter 03, Text 12

SB 6.3.12

yama uvaca
paro mad-anyo jagatas tasthusas ca
 otam protam patavad yatra visvam
yad-amsato ’sya sthiti-janma-nasa
 nasy otavad yasya vase ca lokah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Yamaraja said: My dear servants, you have accepted me as the Supreme, but factually I am not. Above me, and above all the other demigods, including Indra and Candra, is the one supreme master and controller. The partial manifestations of His personality are Brahma, Visnu and Siva, who are in charge of the creation, maintenance and annihilation of this universe. He is like the two threads that form the length and breadth of a woven cloth. The entire world is controlled by Him just as a bull is controlled by a rope in its nose.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The order carriers of Yamaraja suspected that there was a ruler even above Yamaraja. To eradicate their doubts, Yamaraja immediately replied, “Yes, there is one supreme controller above everything.” Yamaraja is in charge of some of the moving living entities, namely the human beings, but the animals, who also move, are not under his control. Only human beings have consciousness of right and wrong, and among them only those who perform sinful activities come under the control of Yamaraja. Therefore although Yamaraja is a controller, he is only a departmental controller of a few living entities. There are other demigods who control many other departments, but above them all is one supreme controller, Krsna. Isvarah paramah krsnah sac-cid-ananda-vigrahah: the supreme controller is Krsna. Others, who control their own departments in the affairs of the universe, are insignificant in comparison to Krsna, the supreme controller. Krsna says in Bhagavad-gita (7.7), mattah parataram nanyat kiñcid asti dhanañjaya: “My dear Dhanañjaya [Arjuna], no one is superior to Me.” Therefore Yamaraja immediately cleared away the doubts of his assistants, the Yamadutas, by confirming that there is a supreme controller above all others.
Srila Madhvacarya explains that the words otam protam refer to the cause of all causes. The Supreme Lord is both vertical and horizontal to the cosmic manifestation. This is confirmed by the following verse from the Skanda Purana:
yatha kantha-patah sutra
 otah protas ca sa sthitah
evam visnav idam visvam
 otam protam ca samsthitam
Like the two threads, horizontal and vertical, of which a quilt is manufactured, Lord Visnu is situated as the vertical and horizontal cause of the cosmic manifestation.
Srimad Bhagavatam Canto 06, Chapter 03, Text 11
Srimad Bhagavatam Canto 06, Chapter 03, Text 13