Manava Dharmashastra 4.112

4.112

śayānaḥ prauḍhapādaś ca kṛtvā caivāvasakthikām
nādhīyītāmiṣaṃ jagdhvā sūtakānnādyam eva ca //

While lying on a bed, while his feet are raised (on a bench), while he sits on his hams with a cloth tied round his knees, let him not study, nor when he has eaten meat or food given by a person impure on account of a birth or a death,