Yōga Sūtra 2.47

प्रयत्नशैथिल्यानन्तसमापत्तिभ्याम्।

prayatnaśaithilyānantasamāpattibhyām।

[प्रयत्न शैथिल्य अनन्त समापत्तिभ्याम्।
prayatna = the effort; śaithilya = by relaxing; ananta = infinite; samāpattibhyām = absorption maintained in parallel;]

Also, it should be possible to relax the effort while maintaining the infinite absorption (in a posture).