﴿ إِذْ نَادَىٰ رَبَّهُۥ نِدَآءً خَفِيًّۭا ﴾

“When he called out to his Sustainer in the secrecy of his heart,”

نِدَاءً خَفِيًّا (a low voice - 19:3) tells us that it is better to beseech Allah in supplication in undertone. Sayyidna Sa'd Ibn Abi Waqqas has narrated that the Holy Prophet ﷺ once said. ان خیر الذکر الخفی ، وخیر الرزق ما یکفی "Surely the best way to make supplication to Allah is in undertone and the best sustenance is that which is sufficient for one's needs (i.e. neither more nor less than required) " (Qurtubi)