Riyad Us-Saliheen (Gardens of the Righteous)

Chapter 134
Excellence of Greeting the Acquaintance Repeatedly

859. Abu Hurairah (May Allah be pleased with him)reported in the Hadith in respect of the person who was at fault in performing his Salat (prayer): He came to the Prophet (PBUH) and greeted him. The Prophet (PBUH) responded to the greeting and said,"Go back and repeat your Salat because you have not performed the Salat (properly).'' He again performed Salat as he had prayed before and came to the Prophet (PBUH) and greeted him. The Prophet (PBUH) responded to the greetings (and repeated his words to him). This act of repeating (the Salat and the Salam) was done thrice.
[Al-Bukhari and Muslim].

Commentary:  This Hadith tells us that one can greet others after short intervals.

860. Abu Hurairah (May Allah be pleased with him) reported: Messenger of Allah (PBUH) said, "When one of you meets a brother (in Faith) he should greet him. Then if a tree or a wall or a stone intervenes between them and then he meets him again, he should greet him.''
[Abu Dawud].

Commentary:  This Hadith convincingly bears out the subject matter of the chapter.