(a) Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) narrates: the Messenger of Allah (peace and blessings be upon him) sent me on an errand. I came to him (after finishing it) and he (peace and blessings be upon him) was praying. I greeted him with salam, and he (peace and blessings be upon him) returned my greeting with a gesture. In the wording of the hadith of Sufyan and others: "He did not reply to me."
(b) By "He did not reply to me" is meant that he did not reply by speaking, but replied with a gesture. Wa billahi al-tawfiq (And success comes only from Allah).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3398