Mu'awiyah bin Hisham narrated it from Sufyan with his chain; he said: I think he attributed it to the Prophet: "There is no deficiency (ghirar) in the salam or in the prayer."
This wording negates slackness in both the salam and the prayer. The earlier hadiths make it permissible to greet someone who is praying and for the one praying to reply with a gesture, and they are more worthy of being followed. Wa billahi al-tawfiq (And success comes only from Allah).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3412