Manavashrautasutra 6.2.2.1

6.2.2.1

asapatnayottamāṃ citim ārabhanta agne jātān praṇudā naḥ sapatnān iti purastāt sahasā jātān praṇudā naḥ sapatnān iti paścāt \\ catuścatvārim̐śī stomas \\ varco draviṇam iti dakṣiṇataḥ sādayati ṣoḍaśī stomas \\ ojo draviṇam ity uttaratas \\ agneḥ purīṣam asi \\ iti purīṣavatīṃ paścāt svayamātṛṇṇāyāḥ //

They begin the topmost layer with an asapatnā [brick]. With “O Agni, repel our born rivals,” [he places one] in the east; with “By might repel our born rivals,” in the west. With “The forty-fourfold stoma / splendor, wealth,” he places [one] in the south; with “The sixteenfold stoma / vigor, wealth,” in the north; with “You are the loose soil of Agni,” [he places] the purīṣavatī [brick] to the west of the naturally perforated stone.