Canto 3 -
Araṇya-kāṇḍa
Chapter 39: Mārīca Describes his Second Encounter with Lord Rāma
Text 3.39.12

ते बाणा वज्रसंकाशाः सुमुक्ता रक्तभोजनाः।
आजग्मुः सहिताः सर्वे त्रयः सन्नतपर्वणः॥

te bāṇā vajra-saṅkāśāḥ sumuktā rakta-bhojanāḥ
ājagmuḥ sahitāḥ sarve trayaḥ sannata-parvaṇaḥ

te = they; bāṇāḥ = of those arrows; vajra-saṅkāśāḥ = and they shone like the lightning; sumuktāḥ = were properly released; rakta-bhojanāḥ = thriving on blood; ājagmuḥ = came; sahitāḥ = together; sarve = all; trayaḥ = three; sannata-parvaṇaḥ = with perfectly smooth joints.

They were properly released and they shone like the lightning. Thriving on blood, all three of those arrows with perfectly smooth joints came together.

“All” indicates that [Lord Rāma] had used them simultaneously.